Preparing stuffed peppers is a two-step process; cooking the filling then baking the peppers stuffed with the filling. Here is the complete process:

• Arrange the peppers: Slice the tops of the peppers and remove seeds to make room for filling.
• Cook the filling: Add some olive oil to a large heavy-bottomed pot and heat it over medium flame. Then add the thin layer of meat when the oil starts to smoke lightly, and sprinkle the salt and pepper.
• Cook with a wooden spoon until the meat browns, which takes 5 to 8 minutes. Then remove the meat from the pot. Stir the onions, garlic, and chili powder into the pot with a little amount of salt. 
• Keep stirring the mixture, and then cook until the flavors meld together. Put the tomatoes gently over medium flame until the tomatoes fall apart and the chili thickens in 12 to 15 minutes. After this, add the meat back into the pot and remove it from the heat.
• Heat the oven: Preheat oven at 400-degree F (204.4°C).
• Bake the peppers: Arrange the peppers on a nonstick baking dish and sprinkle the insides with salt. Also, drizzle with two tablespoons of oil over the dish. Place the baking dish in the center of the oven at 400 F and roast until the peppers are juicy and somewhat softened, and tender. After 15 - 20 minutes, remove the dish from the oven.
• Fill the peppers: Fill each pepper halfway with the freshly cooked filling.
• Finish baking: Top the prepared stuffed peppers with cheese and put them back in the oven for further baking until peppers are tender.