Heat a small amount of olive oil in large frypan, add onions and cook until transparent. Add garlic and mince, cook until mince is browned. Drain fat from pan and discard.
Add the tomato pasta sauce, stir and let simmer until mince is cooked thoroughly.
Preheat oven to 150 degrees C. Grease a baking dish with olive oil spray. Line the bottom of the dish with a lasagne sheet; spread the cottage or ricotta cheese on it, then spread mince over that - approx 2cm thick.
On top of the mince, layer the sliced mushrooms and then a small amount of grated cheese, followed by another layer of the ricotta or cottage cheese. Cover that layer with lasagne and repeat the layers until dish is full or all the ingredients are used. Cover top with extra grated cheese, bake in preheated oven for 45 minutes or until lasagne is soft.