taco casserole recipe

1 pound ground beef or turkey 1 small onion, finely chopped 1 (1 oz) packet taco seasoning mix 1 (15 oz) can black beans, drained and rinsed 1 (10 oz) can diced tomatoes with green chilies, undrained 1 cup frozen corn 1 cup salsa 2 cups tortilla chips, crushed 2 cups shredded cheddar cheese (or your favorite cheese) Optional toppings: sliced green onions, chopped cilantro, sour cream, diced avocado, black olives, and jalapeños