Heat the olive oil in a skillet over medium heat. Add the diced onion and bell pepper, and sauté until softened and fragrant, about 5 minutes. If using turkey bacon, cook it in the same skillet until crispy, then transfer to a paper towel-lined plate to drain. Once cool, crumble the turkey bacon into small pieces.
In a large mixing bowl, combine the cooked pasta, shredded chicken, sautéed onions and peppers, and the BBQ sauce. Sprinkle in garlic powder, onion powder, salt, and pepper. Stir gently until the pasta and chicken are evenly coated.
Fold in half of the shredded cheddar and mozzarella cheeses, along with the crumbled turkey bacon if using.
Transfer the mixture to your prepared baking dish, spreading it into an even layer. Top with the remaining shredded cheddar and mozzarella cheese.
Preheat your oven to 350°F (175°C). Bake the casserole uncovered for 20-25 minutes, or until the cheese is melted, bubbly, and golden brown around the edges.
Allow the casserole to cool for a few minutes before serving. Serve with a simple green salad or roasted veggies for a complete meal.