Firstly, get the onions gently softening in your frying pan in a few squirts of fry light.
While the onions cook, boil the potato slices for 5 minutes before adding the peas and cooking for a further 3. Drain.
Once the onions are soft, add the crushed garlic and cook for 3 more minutes, before adding the peas and potatoes and cooking for another 5 minutes or so.
Whilst the onions, potatoes and peas cook, whisk the eggs, season to taste and stir in the chopped parsley and quartered tomatoes.
Just before you pour in the egg mixture, add the oil to the pan and heat it up before adding the eggs. Turn the ring down to a lowish setting and cook for 7 minutes. Meanwhile, turn the grill onto medium.
Pop the pan under the preheated grill and cook for a further 5 minutes or so. Keep an eye on it: you might want to cook it for longer if the eggs don’t appear to be fully set and cover it with a sheet of foil if the top seems to be browning too quickly.
Remove from grill and leave to cool before loosening tortilla from edges and bottom of pan and turning out onto a plate. Slice and serve warm immediately, or at room temperature later/ next day.