Bring a large pot of salted water to a boil. Add 8 oz of elbow macaroni and cook until al dente, about 7-8 minutes. Drain the pasta and set aside.
In a skillet over medium heat, cook 1/2 cup of turkey bacon pieces until crispy. Remove from the pan and place on paper towels to drain excess fat. Once cooled, crumble into bite-sized pieces.
In a large mixing bowl, combine 1/2 cup mayonnaise, 1/2 cup plain Greek yogurt, 1 tsp garlic powder, and 1/2 tsp black pepper. Stir until smooth and creamy.
Fold in the drained tuna, 1 cup shredded cheddar cheese, 1/4 cup chopped green onions, 1/2 cup chopped bell peppers, and the crumbled turkey bacon. Mix until everything is evenly distributed.
Add the cooked elbow macaroni to the bowl and gently fold everything together until the pasta is well coated with the creamy mixture.
Preheat your oven to 375°F (190°C). Transfer the pasta mixture to a greased 8x8 inch baking dish. Sprinkle 1/2 cup grated Parmesan cheese evenly on top, then add 1/4 cup breadcrumbs for a crunchy finish.
Bake uncovered for 20-25 minutes, or until the top is golden brown and the edges are bubbly. Let it cool slightly before serving.