Place the peppers, cut side up, in a 9" by 13" baking dish. Add about a half cup of water to the bottom of the dish, cover with foil, and bake in a preheated 350 degrees oven for 15 minutes.
Add the ground beef, chopped onion, garlic powder, Italian seasoning, salt, and pepper. Cook while stirring occasionally until the meat is cooked through and the onion has softened.