Bring a large pot of lightly salted water to a boil. Place macaroni in the pot, and cook for 8 to 10 minutes or until al dente; drain.
Preheat oven to 375 degrees F (190 degrees C). Lightly grease a large casserole dish.
Place the ground beef in a skillet over medium heat, and cook until evenly brown. Drain grease. Mix in diced tomatoes, tomato paste, and sloppy joe seasoning. Reduce heat to low, and simmer 10 minutes.
Melt the butter in a large pot over medium-high heat. Stir in the onion, and cook until tender. Mix in flour, mustard, salt, and pepper. In a bowl, mix the half and half and Worcestershire sauce. Gradually whisk half and half mixture into the pot. Bring to a boil, and cook 1 minute, until slightly thickened. Remove from heat. Mix in 3 cups of cheese. Stir cooked pasta into the pot, evenly coating with the sauce. Transfer to the casserole dish. Layer with the beef mixture and top with remaining cheese.
Cover, and bake 30 minutes in the preheated oven. Remove cover, and continue baking 10 minutes, until bubbly.