Step 1

Bring large pot of salted water to boil and cook noodles according to package instructions for al dente. Drain well.

Step 2

Meanwhile, add beef and onion to large high-sided skillet or Dutch oven set over medium-high heat. Cook 6 to 8 minutes or until meat is cooked through, using spoon to break up meat as it cooks. Spoon out and discard any excess grease in pan.  Use slotted spoon to transfer beef mixture to medium bowl.

Step 3

Reduce heat to medium and melt butter in same skillet. Add flour and cook 2 minutes, stirring constantly. While whisking, add milk in steady stream and cook 2 to 3 minutes or until thickened, whisking constantly.

Step 4

Remove from heat. Add taco seasoning and whisk until well combined. Add tomatoes, chiles, cheese, pasta and meat. Stir until well combined and cheese is melted.

Step 5

Serve topped with with crushed tortilla chips, sliced green onions, salsa and sour cream, if desired.