Preheat oven to Gas Mark 4, 180°C (350˚F).
Heat a little oil in a frying pan over a medium heat. Place the prepared peppers, onion, potato, mushrooms and garlic in a bowl and mix with a tablespoon oil. Season with a little salt and black pepper and then add the mixture into the frying pan. Allow the vegetables to cook for 10-15 minutes until softened but not browned. Stir frequently.
Grease mini tortilla. Meanwhile whisk the eggs and milk together. Add ⅔ of the cheese and the parsley. Season with a little salt and black pepper then add in the cooked vegetables. Spoon the mixture into the prepared tins.
Sprinkle over the remaining cheese.
Bake for 8-10 minutes or until tops are golden and the centres are set.
Let them rest for a couple of minutes before serving.