In a large skillet, brown the ground beef over medium heat.
Cook the 12 ounces of dry macaroni according to the package directions. Drain and set aside.
Meanwhile, in a large skillet, brown the ground beef over medium heat . Be sure to crumble the beef into small pieces and season with salt and pepper while cooking. When the beef is done, remove it from the skillet, drain, and set aside.
Return the same skillet to heat, and add bacon and onions. Cook until the bacon is fully cooked and the onions are translucent.
In a two quart casserole dish , combine macaroni, diced tomatoes (do not drain the cans), ground beef, onions, and bacon. Stir to combine.
Top the casserole with both kinds of cheese.
Bake in a 350°F oven until the cheese is melted. You may want to brown the cheese by turning on your broiler function for a moment or two before removing the casserole from the oven.