In a skillet, brown ground beef and onion. Drain. Add salt, garlic powder and pepper. Cut bread lengthwise in half; butter both halves and place on baking sheet. Remove meat mixture from the heat; stir in sour cream. Spoon onto the bread. Sprinkle with tomatoes, green pepper and cheese. Bake at 350 degrees F for 20 minutes or until the cheese is melted (bake longer for crispier bread).
