Fry the lardons or bacon in the oil in a large non-stick frying pan until starting to brown, add the courgettes, then fry for a couple of mins until they begin to soften. Add the sweetcorn and spinach, season if you like, then heat through.
Heat grill to medium. Beat the eggs, then pour over the vegetables. Crumble over the cheese, then cook gently until the egg has just set around the edges, about 5 mins. Slide the frittata under the grill, then cook until the egg is set and the top is lightly browned. Cut into wedges and serve with a simple green salad.