To prepare the meat sauce: Heat one tablespoon oil in a skillet over medium heat. Add the garlic, red pepper strips, diced bell pepper and cook for about 2 minutes, until fragrant and the bell peppers are tender. Add the ground beef. Cook until browned, about 10 minutes, breaking apart the meat with a spoon or spatula.
Stir in marinara sauce and Italian seasoning. Add sea salt and black pepper to taste. Reduce heat to a gentle simmer. Simmer for about 30 minutes while preheating the oven and preparing the peppers.
Meanwhile, preheat the oven to 375 degrees F. Line a baking sheet with foil.
To prepare the peppers, chop off the tops and scoop out the seeds and ribs inside. Slice a tiny layer off the bottoms (without making a hole if possible) so that the peppers are stable standing upright.
To assemble the lasagna cups, layer 1-2 tablespoons each of meat sauce, ricotta cheese, and shredded mozzarella cheese inside the bell peppers. (You'll want a little more meat sauce compared to the other two layers.) Repeat until peppers are filled to the top, with mozzarella being the top layer.
Place the peppers on the lined baking sheet and tent with aluminum foil, making sure the foil is not touching the cheese. Bake for 30 minutes. Remove the foil and bake 10 more minutes, until cheese is melted and browned.