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A close-up of a classic green bean casserole in a white serving dish, topped with golden crispy fried onions.

High Protein Green Bean Casserole

This elevated take on classic green bean casserole is packed with protein, featuring a creamy, homemade mushroom sauce and crispy baked onion topping, without compromising on flavor or comfort.
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Prep Time 45 minutes
Cook Time 25 minutes
Total Time 1 hour 10 minutes
Servings: 8 servings
Course: Dinner, Side Dish
Cuisine: American, Comfort Food
Calories: 220
Ingredients Equipment Method Notes

Ingredients
  

For the Green Bean Casserole
  • 2 lbs Fresh green beans trimmed and snapped
  • 1 tbsp Olive oil
  • 8 oz Cremini mushrooms sliced
  • 1/2 medium Yellow onion finely chopped
  • 2 cloves Garlic minced
  • 1/4 cup All-purpose flour
  • 1 1/2 cups Low-sodium chicken broth
  • 1 cup Plain non-fat Greek yogurt
  • 1/2 cup Grated Parmesan cheese
  • 1 tsp Dried thyme
  • 1/2 tsp Onion powder
  • 1/4 tsp Black pepper
  • 1/4 tsp Nutmeg ground
  • 1/2 tsp Salt or to taste
  • 1/4 cup Unflavored whey protein isolate optional, for extra protein boost, omit if not desired
For the Crispy Air-Fried Onions
  • 1 large Yellow onion very thinly sliced into rings
  • 1 tbsp Olive oil
  • 2 tbsp All-purpose flour
  • 1/2 tsp Smoked paprika
  • 1/4 tsp Garlic powder
  • 1/4 tsp Salt

Equipment

  • Large Skillet
  • 9x13 inch baking dish
  • Whisk
  • Cutting board
  • Sharp knife
  • Measuring cups and spoons
  • Small Bowl
  • Air Fryer
  • Large Pot

Method
 

Green Bean Preparation
  1. Bring a large pot of salted water to a boil. Add the trimmed green beans and blanch for 3-5 minutes, or until bright green and tender-crisp. Immediately drain and plunge into an ice bath to stop cooking. Drain thoroughly and set aside.
High-Protein Creamy Sauce Preparation
  1. Preheat your oven to 375°F (190°C). Grease a 9x13 inch baking dish.
  2. In a large skillet over medium heat, add 1 tbsp olive oil. Add the sliced mushrooms and cook for 5-7 minutes, stirring occasionally, until they release their liquid and start to brown. Add the finely chopped yellow onion and cook for another 3-4 minutes until softened.
  3. Stir in the minced garlic and cook for 1 minute until fragrant. Sprinkle in the 1/4 cup all-purpose flour (and optional whey protein isolate if using) and cook, stirring constantly, for 1-2 minutes to create a roux.
  4. Gradually whisk in the low-sodium chicken broth, ensuring no lumps form. Bring the mixture to a simmer, stirring, until it thickens. Remove from heat.
  5. Stir in the Greek yogurt, Parmesan cheese, dried thyme, onion powder, black pepper, ground nutmeg, and salt. Taste and adjust seasoning as needed. The sauce should be creamy and flavorful.
Casserole Assembly and Baking
  1. Add the blanched green beans to the creamy sauce in the skillet and toss gently to coat evenly. Pour the green bean mixture into the prepared baking dish, spreading it into an even layer.
  2. Bake in the preheated oven for 15 minutes while you prepare the crispy onions.
Crispy Air-Fried Onions Preparation
  1. While the casserole bakes, prepare the crispy onions. In a medium bowl, toss the very thinly sliced large yellow onion rings with 1 tbsp olive oil until lightly coated.
  2. In a separate small bowl, combine the 2 tbsp all-purpose flour, smoked paprika, garlic powder, and salt. Add this mixture to the onions and toss until all onion rings are evenly coated.
  3. Preheat your air fryer to 375°F (190°C). Arrange the coated onion rings in a single layer in the air fryer basket (you may need to do this in batches).
  4. Air fry for 8-12 minutes, shaking the basket halfway through, until golden brown and crispy. Watch closely as they can burn quickly. If using an oven, spread on a baking sheet and bake at 400°F (200°C) for 15-20 minutes, flipping halfway.
Finish and Serve Casserole
  1. Remove the casserole from the oven. Evenly sprinkle the freshly made crispy air-fried onions over the top. Return to the oven for another 5-10 minutes, or until the topping is golden and the casserole is bubbly.
  2. Let stand for 5 minutes before serving hot. Enjoy your delicious High Protein Green Bean Casserole!

Notes

For an even richer flavor, you can use a splash of dry white wine to deglaze the pan after cooking the mushrooms and onions. If you don't have an air fryer, the crispy onions can be baked in a regular oven at 400°F (200°C) for 15-20 minutes, flipping halfway. Store leftovers in an airtight container in the refrigerator for up to 3-4 days. This recipe is perfect for holidays or a healthy weeknight side.