Beat the egg in a mixing bowl, then add the ground beef, tomatoes, and crushed crackers. Season with onion flakes, garlic powder, seasoned salt, and pepper. Mix until evenly combined. Pack into a 9x5 inch loaf pan.
Bake in the preheated oven until no longer pink in the center, about 1 hour. An instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C).