Preheat your oven to 350°F and spray a 9x13-inch baking dish with cooking spray.
In a large skillet over medium-high heat, brown the ground beef with the diced onion until the meat is fully cooked and the onion is soft. Drain any excess fat.
In a large mixing bowl, combine the cooked noodles, beef mixture, cheese soup, sour cream, 1½ cups of the shredded cheese, chopped pickles, ketchup, and mustard. Season with salt and pepper.
Transfer the mixture to your prepared baking dish and spread it out evenly.
Top with the remaining ½ cup of cheese and sprinkle the crushed crackers over the top.
Bake uncovered for 25-30 minutes until bubbly and the top is golden brown. Let it rest for 5 minutes before serving.