Preheat oven to 425 degrees and spray a rimmed baking sheet with cooking spray.
Combine ground beef, Panko crumbs, 1 1/2 tablespoons Bulgogi sauce, ginger, white parts of green onion, salt, and pepper in a medium bowl. Gently mix until evenly combined.
Shape into 1 1/2-inch meatballs and place on baking sheet. You should get about 12.
Bake for 15 minutes.
Place meatballs in a bowl and gently toss them with Bulgogi sauce. Sprinkle with sesame seeds and green part of green onions.
In a small bowl, stir together sour cream, water, and Sriracha sauce. Drizzle over meatballs and serve with rice.