Clean the mushrooms and peal the onion and garlic cloves. Slice the mushrooms and the garlic into slices. Cut the onion into strips.
Assemble the other ingredients. Add some oil to the bottom of the baking pan.
Start with a mushroom layer. use 1/3 of the mushrooms, 1/3 of the garlic and 1/3 of the red onion. Salt and pepper everything, then add the first layer of lasagne sheets.
Cover them with dollops of 1/2 of the cream cheese topped with all of the French Brie, cut or torn into pieces. Add another layer of mushrooms, garlic and onion. Salt and pepper again and top them off with the remaining lasagne sheets.
Cover them with the remaining cream cheese. Finish with a final layer of mushrooms, garlic and onion, topped with pesto dollops.
Cover everything with the Mozzarella and bake in a pre-heated oven at 200 degrees Celcius for 35-40min or until the cheese on the top turns the desired colour.
Leave the lasagne to cool for at least 10 minutes before you cut into it! Enjoy!