Step 1

Bring a large saucepan of water to the boil, add the squash and cook for 10–15 minutes, until tender. Drain.

Step 2

Meanwhile, in a large bowl, beat together the eggs, milk and mustard and season.

Step 3

Heat a large (20 cm/8 inch) non-stick frying pan and spray with the cooking spray. Add the squash and stir fry for a few minutes, until it turns golden. Add the spinach and stir fry for a further few minutes, until wilted. Tip the egg mixture into the pan.

Step 4

Stir gently together and then cook over the lowest heat, without stirring, for 10–12 minutes or until the bottom is golden and the tortilla is nearly set. Preheat the grill to medium.

Step 5

Slide the pan under the preheated grill for a few minutes, until the top is golden and puffy and the egg is completely set. Cut into four wedges and serve.