01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish.
02 - Boil elbow macaroni in a large pot according to package instructions. Drain well and set aside.
03 - In a large skillet over medium heat, cook ground beef until thoroughly browned. Drain off excess fat.
04 - Add onion and red bell pepper to the skillet. Sauté for 3 to 4 minutes until softened.
05 - Stir in taco seasoning, black beans, diced tomatoes with green chilies, and frozen corn. Cook an additional 2 to 3 minutes, then remove from heat.
06 - In a saucepan over medium heat, melt butter. Whisk in flour and cook for 1 minute. Gradually add milk, whisking until slightly thickened, about 2 to 3 minutes.
07 - Incorporate cream cheese and 1 1/2 cups shredded cheddar cheese. Stir until sauce is smooth and melted.
08 - In a large mixing bowl, combine cooked macaroni, beef-vegetable mixture, and cheese sauce. Mix thoroughly and season with salt and pepper.
09 - Transfer mixture into the prepared baking dish. Top evenly with the remaining 1/2 cup cheddar cheese and crushed tortilla chips, if using.
10 - Bake uncovered for 20 to 25 minutes until casserole is hot, bubbly, and golden. Allow to rest for 5 minutes before serving.