Preheat the oven to 180°C.
Finely grate the courgette. Remove the skin of the chorizo sausage, then chop the flesh into tiny pieces.
Whisk the eggs, then add the chorizo & courgette. Season with salt and pepper. Add the chilli flakes, if used.
Spray 6 silicon muffin cases with cooking spray.
Drain and tear the mozzarella into small pieces. Add third of it to the egg mixture.
Divide the mixture evenly between the cups. Put a couple of basil leaves on top of each cup, then cover them with the remaining mozzarella.
Bake for approx. 15 minutes, until the egg has set and cheese has melted and browned.
Garnish with basil leaves and drizzle with balsamic glaze before serving.