Thinly slice the bell pepper and halve the tomatoes.
Heat the oil in a non-stick frying pan. Add the pepper slices and gently sauté for 5-8 minutes, until tender, then add the tomatoes. Cook for another 3 minutes.
When the tomatoes have softened stir in the peas and garlic. Put a lid on and steam for 2-3 minutes.
Meanwhile, whisk the eggs with the chopped mint and some salt and pepper. Add the chilli flakes, if used.
Crumble the goats cheese into a small bowl.
Pour the egg over the peas, pepper and tomato pieces, letting it spread out evenly. Scatter the cheese crumbles on top - if used.
Put a lid on and cook for about 5, then turn down the heat and cook until the surface has set.
If needed, or you want the cheese to be brown, turn on the grill in the oven and brown the frittata for a couple of minutes.
Let the frittata cool a bit, then serve, garnished with mint leaves. Or let it cool completely and cut it into squares.