Cook the elbow macaroni according to package instructions in a large pot of salted boiling water. Drain and set aside.
In a large skillet over medium heat, add the ground beef and cook until browned and fully cooked, breaking it apart as it cooks. Drain excess fat if necessary.
Stir in the taco seasoning, black beans, and corn, mixing well. Cook for about 2-3 minutes until heated through. Remove from heat and set aside.
In the same pot used for macaroni, melt the butter over medium heat. Once melted, add flour, stirring to combine and cook for about 1 minute to create a roux.
Slowly whisk in milk and garlic powder, seasoning with salt and pepper. Continue whisking until the mixture thickens (about 3-5 minutes).
Once thickened, add 1½ cups of shredded cheddar cheese and stir until melted and creamy.
Combine the cooked macaroni with the cheese sauce, stirring well. Fold in the beef mixture until evenly combined.
Transfer the mac and cheese mixture to a greased 2-quart baking dish. Top with the remaining ½ cup of shredded cheddar cheese.
Bake in a preheated oven at 350°F (175°C) for 15 minutes, or until the cheese is bubbly and golden brown.
Remove from oven and let cool for a few minutes. Serve warm and garnish with fresh cilantro and jalapeños if desired.