Preheat oven to 350 degrees F.Spray a 9x13-inch casserole dish with cooking spray.Add cubed american cheese and crushed nacho-flavored tortilla chips,mix well.
Heat a large skillet over medium-high heat and stir in ground beef,chopped green chiles,diced red onion and 1/2 package taco seasoning.Cook and stir mixture until the beef is crumbly,evenly browned,and no longer pink,about 10 minutes.Drain and discard any excess grease.
Combine remaining taco seasoning with cream cheese,cheddar cheese soup and evaporated milk in a saucepan;heat soup mixture until just boiling.
Layer tater tots in the prepared casserole dish.
Bake in the preheated oven until tater tots begin to crisp and cheese is melted,about 10 minutes.
Spoon ground beef mixture over tater tots;pour into soup mixture.
Bake until soup mixture is bubbling,15 to 20 minutes.Sprinkle casserole with mexican cheese blend;bake until cheese is melted,5 to 10 minutes.