Place the eggplant slices in a colander, sprinkle with salt and leave for 20 minutes while you are preparing the other vegetables. Rinse under cold water, drain and reserve.
Heat the oil in a pan and saute the garlic and onion for 1 to 2 minutes.
Add the peppers, mushrooms, celery and zucchini and cook for 3 to 4 minutes, stirring.Stir in the spices and cook for 1 minute.
Mix together the tomatoes, passata, basil and season well.For the sauce, melt the butter in a pan, add the flour and cook for 1 minute.
Remove from the heat and stir in the stock and milk. Return to the heat and add half the cheese and mustard. Boil, stirring until thickened. Stir in the basil and season to taste.
Remove from the heat.
Add a bit of the hot mixture to the beaten egg to temper it, then stir the whole mixture back into the cheese sauce, Set aside.Coat the bottom of a square baking dish with some of the tomato sauce and place half of the lasagna sheets in the dish. cover with half the vegetables, then half the tomato sauce, and finally half the eggplant. Repeat again, spooning the cheese sauce on top of everything.
Sprinkle with the remaining cheddar cheese.Cook in a preheated oven 180*C/350*F for 40 minutes until browned and bubbly.