1 pound ground beef
1 teaspoon vegetable oil, or as needed
1 onion, diced
2 cloves garlic, chopped
1 (10 ounce) can diced tomatoes with green chile peppers (such as Rotel) drained
1 cup salsa, drained
1 (7 ounce) can Mexican-style corn, drained
1 cup sour cream
3 cups shredded Cheddar cheese, divided
1/2 teaspoon salt
1/4 teaspoon ground black pepper
Preheat oven to 350 degrees F (175 degrees C).
Heat a large skillet over medium-high heat. Cook and stir beef in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease. Transfer ground beef to a 9×13-inch casserole dish.
Heat oil in a skillet over medium heat; cook and stir onion and garlic in the hot oil until onion is translucent, about 10 minutes. Spoon onion mixture over ground beef.
Mix tomatoes with green chile peppers, salsa, corn, sour cream, 1 cup Cheddar cheese, salt, and black pepper into ground beef mixture; top with remaining 2 cups Cheddar cheese.
Bake in the preheated oven until cooked through and cheese is melted, about 45 minutes. Let stand for 10 minutes before serving.
Serve with a dollop of sour cream, sliced black olives, more salsa, and warmed tortillas.