Preheat the oven to 375 degrees. Cook the macaroni in a large pot of boiling water until just tender, then drain and set aside.
While the pasta cooks, place the bacon in a skillet over medium heat and cook until crisp. Remove the bacon to a plate, let it cool, and crumble it into pieces.
In a saucepan over medium heat, melt the butter. Whisk in the flour and cook for one minute. Slowly pour in the milk while whisking to avoid lumps. Continue cooking until the mixture thickens.
Remove the saucepan from the heat and stir in the cheddar cheese, salt, and pepper until the cheese melts into a smooth sauce.
Combine the cooked macaroni, cheese sauce, frozen peas, and half of the crumbled bacon in a large bowl. Stir gently to coat everything evenly.
Transfer the mixture to a baking dish. Sprinkle the breadcrumbs and remaining bacon over the top.
Bake for 20 minutes until the top turns golden and the edges bubble.