StirBlue, your lasagne recipe sounds intriguing.
I've never tried frozen onions.
Mushrooms don't really have a "season", unless you are buying some wild variety that cannot be cultivated. "Button" mushrooms take two weeks to mature, from "planting" to harvesting. There's a really interesting eppy of "Dirty Jobs" that shows how mushroom farmers work. All they really have to do is split their total growing volume into two different times, and "plant" one half one week, the second half the second week, harvest and replant the first one the third week, harvest and replant the second half the fourth week, etc., ad naseum.
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!