Mash potato with a little milk. Add half the grated cheese, stir, add half the tomatoes, onion if using and the bacon loin, stir. Put into baking dish. I use one 2 inches deep by 8x8 inches wide. Flatten, top with remaining tomatoes, bacon laid out to cover tomatoes, sprinkle with cheese, then put in oven until cheese melted and bacon crisping up....about 20 mins less if grilling...about 15.