Preheat oven: Heat oven to 375°F (190°C). Lightly grease a baking dish.
Prepare peppers: Blanch bell peppers in boiling water for 3 minutes to soften slightly. Drain and set aside.
Cook filling: In a skillet, heat olive oil over medium heat. Sauté onion and garlic until softened. Add chopped shrimp and cook until pink, about 2–3 minutes.
Mix stuffing: In a large bowl, combine cooked shrimp, crab meat, rice, cream cheese, Parmesan, mayonnaise, Old Bay, salt, and pepper. Stir until creamy.
Stuff peppers: Spoon seafood mixture evenly into the prepared bell peppers. Place peppers upright in the baking dish.
Top and bake: Sprinkle shredded cheese on top of each pepper. Bake for 20–25 minutes until peppers are tender and cheese is melted and golden.
Serve: Garnish with lemon wedges and fresh herbs, if desired.