Preheat oven to 350*

Fry hamburger and finely diced onion together and drain.

Spray a very large lasagna pan with Pam.

Spoon small amount of spaghetti sauce on bottom of pan.

Layer noodles, then ricotta or cottage cheese, then hamburger, mushrooms, parmesan, sauce, and then mozzarella.

Repeat layers until pan is full, cover with tin foil and bake 45 minutes to an hour.