In a large pan, saute the onions and mushrooms in a tablespoon of olive oil or butter until the mushrooms are golden brown.
Add the garlic, herbs and lemon juice and cook for another minute or two until the garlic is fragrant. Season to taste and set aside.
Combine the cheese sauce, sour cream and cheese.
Assemble the lasagna by layering the mushrooms, cheese sauce, pasta sheets and grated cheese in a baking dish. Cover with foil and place in the oven.
Allow to bake for 40-45 minutes or until the lasagna sheets are fully cooked. Remove the foil then bake for another 10-15 minutes until the top is golden brown.
Remove from the oven and allow to rest for 10 minutes before serving.