In a medium bowl, combine the meat, 4 tablespoons of the enchilada sauce and seasoning. Divide the meat into four equal balls.

On a flat top grill or large cast iron skillet, over medium high heat, add the serrano and onion. Let cook until the pepper is blistered and the onions are slightly charred and softened. Remove from the heat. Remove the skin from the pepper and cut into thin strips.

Butter both sides of the tortillas and buns and place on the warm side of the grill to toast. Be careful not to over toast the tortillas or they will become brittle. Top 2 of the tortillas with 1 slice of cheddar cheese each, to melt slightly. Place the buns and tortillas in a warm place.

Place the ground beef on the grill plate or skillet. Place a piece of wax paper on top and flatten with a press. Remove the paper. Cook for about 2 minutes, then flip over and cook for another 1 minute, or until browned. Top 2 patties with 1 slice of the colby cheese each, to melt slightly.

Add about 1 to 2 tablespoons of the enchilada sauce to the bottom bun. Top with 1 tortilla/cheese, followed by a hamburger patty, tortilla, onions and pepper slices, another corn tortilla and hamburger patty, 1 to 2 tablespoons of enchilada sauce and top with the bun. Repeat with the remaining ingredients. Serve.