Preheat the oven to 350°F.
In a medium skillet, cook the ground beef and diced onion over medium heat, seasoning with salt and black pepper to taste. Drain the grease.
In the casserole dish, combine the cooked beef mixture, drained tomatoes, and shredded potatoes.
Stir in the special sauce and evenly top with shredded cheese.
Bake the casserole uncovered at 350°F for 30 minutes, or until the potatoes are tender and the cheese is set and starting to bubble at the edges.
Cool the casserole for 10 minutes on the counter before serving.