Brown ground beef in a large deep skillet, stirring to crumble. Drain beef well, and set aside. Wipe skillet clean.
Return beef to skillet; stir in beans, chiles, and seasoning mix.
Cook over medium-low heat, stirring often, until thoroughly heated.
Press each tortilla into a tortilla shell pan or 1-quart oven-safe bowl.
Bake at 375° for 8 to 10 minutes or until crisp. Place on lettuce-lined serving plates. Spoon bean mixture evenly into shells; sprinkle with cheese and diced tomato. Serve with desired condiments.