Heat olive oil in an 8-inch oven-safe skillet over medium heat. Add zucchini and celery and cook, stirring, for 5 minutes or until softened and light golden. Meanwhile, whisk together milk and eggs in a bowl and season with freshly ground black pepper.

Reduce the heat to low and pour egg mixture into the pan. Stir gently for 20 seconds, then leave to cook, untouched, for 8 minutes or until the edges have set firm but the top and center are still runny.

Preheat the oven broiler to high. Sprinkle the cheddar over the egg mixture, then place the pan under the broiler for 2 to 3 minutes or until the cheese is melted and golden and the center is completely set when tested with a knife.

Stand for 5 minutes, then cut in half and scatter with the combined spinach and basil. Serve each portion with two pieces of toast alongside.