Heat oil in frying pan and add mushrooms. Cook until softened. Remove from heat and add pesto and stir through.
Assemble lasagne in baking dish by layering mushroom mixture, bechamel sauce and lasagne sheet. Continue and end with bechamek sauce.
Cover with foil and bake in a at 200 degrees celsuis for 30 minutes. Remove foil and place back in over for a further 5 minutes.
Server with a nice crisp salad.