Preheat the oven to 350°F. Spray a 9 x 13 inch baking dish with cooking spray. Set aside. In a large pot of boiling salted water, cook the pasta according to the package directions for al dente (about 5-7 minutes) and drain well.

In a large skillet, heat the oil over medium-low heat. Add the onions and cook until lightly golden and soft, about 4-5 minutes. Stir in the garlic and cook for 30 seconds. Stir in the beef and cook until browned; season with salt and pepper. Stir in the tomato paste or marinara sauce and tomatoes and mustard. Allow to cook on medium heat for about 5 minutes.

After the pasta and meat are cooked Toss the meat mixture with the pasta and spread it into the prepared dish. Top with the cheddar cheese and bake for 10-12 minutes or until the cheesy is fully melted and the casserole is boiling in the edges. Remove from oven and Sprinkle the chopped pickles over the top and serve.