Preheat the oven to 350°F (180°C).
Line a baking sheet with aluminum foil and arrange the clams on top. This will help capture any juices that may escape during cooking.
In a large skillet, cook the diced bacon until crispy. Remove the bacon from the pan and set aside.
In the same pan, melt the butter over medium heat. Add the chopped red bell pepper, yellow onion, celery, and garlic. Cook until softened, about 5 minutes.
Add the cooked bacon back into the pan with the vegetables. Season with salt and pepper and mix well.
In a small saucepan, melt the butter over low heat. Add the bread crumbs and mix until coated in butter.
Add the grated parmesan and parsley to the bread crumb mixture and stir well.
Spoon the vegetable and bacon mixture onto each clam. Top with the breadcrumb mixture.
Bake for 10-15 minutes, until the breadcrumbs are golden brown.
Serve the Clams Casino with lemon wedges on the side.