Rub 1 tbsp. of butter on the bottom and sides of an eight-inch skillet. Cut the rest into small pieces.
Cut the potatoes and tomatoes into 1/4-inch thick slices.
Core and seed the bell pepper. Roughy chop along with the onion.
Arrange the potato slices around the outer edge of the skillet, the slices slightly overlapping one another.
Make a similar inner circle with the tomato slices making sure that the center of the skillet remains unfilled.
Fill the hollow center with the chopped bell pepper and onion.
Sprinkle everything generously with salt and pepper.
Dot with the remaining butter.
Set the pan over medium heat. Cover after three minutes to create enough steam to soften the pepper and onion pieces a little. Cook for two to three minutes.
Pour in the beaten egg or eggs. Continue cooking, uncovered, for another minute or two or until the eggs are set.
Turn off the heat. Squeeze the lemon quarter over everything. Sprinkle the vegetables with grated cheese and chopped parsley.