Preheat the oven to 180°C. Brush a 24cm round baking dish with oil.
Bring a small saucepan of water to the boil and cook the eggs for 10 minutes. Drain and rinse under cold water before peeling and slicing into quarters.
Melt the butter over a moderate heat in the same saucepan and mix in the flour, cook stirring for 2 minutes before gradually adding the milk, whisking continuously until the mixture bubbles and thickens. Remove from the heat and stir through the mayonnaise
Lay a tortilla in the base of the baking dish and cover with half of the red onion, celery, tuna and sliced egg. Spoon over a third of the sauce, sprinkle with a third of the cheese, half the parsley and season with salt and pepper.
Cover with the another tortilla and repeat the process
Finish off with a tortilla on top, spread with the sauce and sprinkle with the remaining cheese.
Bake for 20 minutes until the top is crisp and golden. Serve with a green salad.
Video
Notes
If you don’t have a large round baking dish then just trim the tortilla wraps and arrange the pieces in a rectangular dish eg; a lasagne dish or similar.