Preheat the oven to 375 degrees F. Coat an 8 inch or 2 quart baking dish with cooking spray.
Cook macaroni in salted water according to package directions.
Place the bacon in a large pan over medium high heat. Cook for 5-6 minutes or until bacon is browned and crisp.
Remove bacon from the pan and set aside.
Drain off most of the bacon fat, leaving 2 teaspoons remaining in the pan.
Add the ground beef to the pan and season generously with salt and pepper to taste.
Cook, breaking up the meat with a spatula into small pieces, until browned. This should take 4-5 minutes.
Add the onion and cook for an additional 4-5 minutes, or until onion has softened.
Add the tomato sauce, ketchup, mustard and half of the bacon to the pan. Stir to coat the ground beef with the sauce.
Drain the macaroni and add it to the pan with the beef mixture.
Add half the cheddar cheese to the pan with the pasta; stir until everything is combined and cheese is melted.
Pour the pasta mixture into the prepared dish. Top with the remaining cheese.
Bake for 15 minutes or until cheese is melted and casserole is bubbly.
Top with reserved bacon and parsley, as well as other toppings such as diced tomatoes, shredded lettuce and chopped pickles.
Let stand 5 minutes, then serve.