In a small bowl, whisk together the honey, soy sauce, minced garlic, rice vinegar, sesame oil, and grated ginger until well combined. This is your honey garlic marinade.

Pat the pork tenderloin dry with paper towels. Season generously with salt and pepper. Place the pork in a large shallow dish or a resealable plastic bag. Pour about half of the honey garlic marinade over the pork, ensuring it's evenly coated. Reserve the remaining half of the marinade for the glaze. Marinate in the refrigerator for at least 30 minutes, or up to 4 hours.

Preheat your oven to 400°F (200°C). If desired, heat olive oil in an oven-safe skillet over medium-high heat. Sear the pork tenderloin for 2-3 minutes on all sides until golden brown. This step is optional but adds a nice crust and color.

Transfer the pork tenderloin (in the skillet or a roasting pan) to the preheated oven. Roast for 15-20 minutes, or until an internal temperature of 145°F (63°C) is reached with a meat thermometer. Halfway through cooking, baste the pork with some of the pan juices, if any.

Once cooked, remove the pork from the oven, transfer it to a cutting board, and tent loosely with foil. Let it rest for 5-10 minutes before slicing. This allows the juices to redistribute, ensuring a tender and moist result.

While the pork is resting, pour the reserved half of the honey garlic marinade into a small saucepan. Bring to a simmer over medium heat. If you prefer a thicker glaze, in a small bowl, whisk together the cornstarch and cold water to create a slurry. Pour the slurry into the simmering marinade, whisking constantly. Continue to simmer for 1-2 minutes until the glaze thickens to your desired consistency.

Slice the rested pork tenderloin into 1/2-inch thick medallions. Arrange on a serving platter and generously drizzle with the warm honey garlic glaze. Garnish with sliced green onions and toasted sesame seeds, if using. Serve immediately with your favorite sides.