Heat the oven to 350 degrees and coat a 9 x 13 inch baking dish with cooking spray. The dish should be ready before the hot pasta and sauce come together so nothing sticks while you assemble.

Boil the rotini in salted water until al dente, then drain it well. The pasta should still have a little firmness since it will keep cooking in the oven.

Warm the olive oil in a large skillet over medium-low heat, then cook the onions for about 5 minutes until softened before adding the garlic for 30 seconds. The onions should look translucent and smell sweet, and the garlic should be fragrant without browning.

Add the ground beef, break it up, and cook until no pink remains, then season with the salt and black pepper. Let the meat brown instead of steaming so you build deeper flavor in the pan.

Stir in the tomato paste, then add the diced tomatoes and Dijon mustard and simmer for about 2 minutes. The sauce should bubble gently and thicken slightly around the meat instead of looking watery.

Combine the drained pasta with the beef mixture and spread everything into the prepared baking dish. You want the pasta evenly coated so every scoop gets sauce, beef, and that burger-style tang.

Scatter the cheddar over the top and bake for about 15 minutes, then finish with the chopped dill pickles before serving. The cheese should be fully melted and the casserole hot throughout, with the pickles adding a fresh, briny bite at the end.