Preheat the oven to 180°C.
Carefully wash and finely dice the aubergines and peppers.
In a frying pan, heat the olive oil and cook the chopped onion. Add the pepper and aubergines and cook for about 15 minutes.
Add the tomato coulis, mix, and reduce the heat.
Meanwhile, in a saucepan, melt the diced butter. Gradually add the flour, stirring well. Then pour the milk onto the butter/flour mixture, whisking everything briskly until the flour thickens.
Season with salt and pepper.
Dice the mozzarella finely.
In a lasagne dish, place a layer of sauce and a layer of pasta, sprinkle with a few cubes of mozzarella and cover with béchamel sauce.
Continue layering to the top of the dish and finish with a layer of sauce covered with pesto, mozzarella and finally béchamel sauce.
Bake in the oven for 30 minutes. Leave to cool for 5 minutes before serving and sprinkle with grated parmesan.