Preheat oven to 350°F. Spray a 9 x 13 inch baking dish with cooking spray.

In a large pot of boiling salted water, cook the rotini pasta until al dente and drain.

In a large skillet, heat olive oil over medium heat. Add chopped onions and cook until soft, about 5 minutes. Stir in garlic and cook for 30 seconds.

Add ground beef to the skillet, season with salt and black pepper, and cook until browned.

Stir in tomato paste, chopped tomatoes, and mustard. Gently simmer for 2 minutes until slightly thickened.

Combine the meat mixture with cooked pasta and transfer to prepared baking dish.

Sprinkle cheddar cheese over the top and bake for 15 minutes until cheese melts. Garnish with chopped pickles and serve.