Preheat the oven to 375 degrees F.
In a large skillet, cook the ground beef over medium-high heat until browned.
Drain any excess grease, and add the onion, mustard, ketchup, salt, and pepper. Cook for a few more minutes, occasionally stirring, until the onion is softened.
Stir in the diced tomatoes and their juice, and cook for a few more minutes.
Meanwhile, unroll the crescent rolls and place them in an 8x8-inch baking dish, pressing them into the bottom and sides.
Spread the beef mixture over the crescent rolls, and sprinkle with the shredded cheese.
Bake for 15-20 minutes, or until the cheese is melted and bubbly.
Serve hot!