In a large skillet over medium heat, melt the butter; saute the onion and bell pepper until tender. Add ground beef and cook, stirring, until beef is browned. Add the garlic and cook for 1 minute longer. Drain off excess fat. Stir in the cumin and chili powder.
In a saucepan, melt the cheese with the tomatoes.
Just before serving, shred the lettuce. Put the lettuce in a large serving bowl. Add diced tomatoes. Crush the corn chips in to the bowl and add the beef mixture. Pour the melted cheese mixture over all and mix to blend ingredients. Serve immediately.
Serves 6 to 8
Calories per serving, based on 8 servings: 534