Preheat oven to 375 degrees F (190 degrees C). Spray a 12-cup full-size muffin tin with cooking spray, and set aside.
Place meat in a large bowl, and break up with a fork. Mix in stuffing, milk, egg, Italian seasoning, garlic powder, red pepper flakes, salt, and pepper until just combined.
Scoop mixture equally into the 12 muffin cups, pressing down firmly on the bottom (using the bottom of a small glass works well) and up the sides, and spoon in some chili sauce. Make a well in the center of each, and spoon in some chili sauce.
Bake uncovered in the preheated oven until cooked through, about 15 minutes. Evenly sprinkle each muffin cup with mozzarella, return to the oven, bake until cheese melts, 3 to 5 minutes more.
Remove from the oven when an instant read thermometer, inserted into the center, reaches 160 degrees F (71 degrees C) and let rest for 5 minutes. Run a knife around the inside of each cup to loosen the meat, remove from muffin tin, garnish with a sprinkle of Italian seasoning, and serve.
