Whisk the eggs in a bowl with the garlic and most of the Parmesan.
Rinse the spinach and put it in a frying pan. Pour some boiling water on to, put a lid on and let it wilt, then drain through a sieve, squeezing the water out of it.
Heat some oil in the frying pan. Add the egg mixture and let it spread out. Cook for a minute then lay the roasted pepper on top (you can slice this beforehand, if you prefer). Then scatter the spinach all over and put the lid on. Turn the heat down and cook for about 10 minutes, until the egg has set.
Turn the grill on. Scatter the remaining cheese on top and brown the frittata under the grill for a couple of minutes. Transfer it to a serving plate and cut into wedges.
Serve hot or cold.