In a medium skillet, melt butter over medium heat. Add garlic, onion, and green pepper and sauté until onions are soft. Preheat oven to 375 degrees F (190 degrees C). In a large mixing bowl, place ground beef, crushed crackers, Cheddar cheese, taco seasoning, and sautéed onion and green pepper. Mix thoroughly. Press beef mixture into a 9x5 inch loaf pan. Bake in a preheated oven for 45 to 55 minutes or until done. Check with a meat thermometer for doneness. Internal temperature should read 165 degrees F (74 degrees C).