Sauté the beef and garlic in a frying pan set over medium-high heat. Add the ricotta cheese and marinara sauce and stir. Add pepper, salt, and Italian seasoning. Allow to cook for a few minutes and remove from heat.
Cut open the bell peppers and empty any contents. Boil water in a cooking pot over high heat and put in the bell peppers. Allow it to sit in boiling water for 5 minutes.
Remove the peppers and stuff each with the ricotta and beef mixture. Place the mozzarella cheese on top of the beef mixture and set in the preheated oven. Allow it to bake for about 30 minutes.