Recipe: Cheeseburger Pasta Casserole

Name: Recipe: Cheeseburger Pasta Casserole
Ingredients: 1 tablespoon olive oil; 1 cup diced yellow onion, plus more for serving; 1 teaspoon kosher salt; 1 pound ground beef, preferably ground sirloin; 2 cloves garlic, minced; 1/2 teaspoon freshly ground black pepper; 1 tablespoon yellow mustard; 1 (14-ounce) can diced tomatoes, drained; 8 ounces dry rotini pasta; 3 cups low-sodium chicken broth; 2 1/2 cups shredded mild cheddar cheese, divided; For serving : Iceberg lettuce, chopped dill pickles