Depends how many you're cooking for, I think.
Well you could knock up a brisk chicken Jalfrezi with the chicken, half the onion, couple of cloves of garlic and the peppers. Dice the onion and peppers, fry onions in oil for a couple of minutes, add peppers and fry for a couple of minutes, add spices, squeeze of tomato puree, leftover chicken. Boiled rice with it.
Pasta, the tin of toms, a carrot, the other half of the onion and some garlic the and mushrooms for a sauce. Dice and fry the onion for a couple of minutes, dice and add the carrot, add the tin of tomatoes to the mix, rinse the tomato tin out with water and add half a tin worth of water to the mix, add a little rosemary and some oregano and tomato puree if you have it, leave to simmer on a very low heat for 30 minutes or so to allow the flavours to come together, boil up your water for pasta. Then once the pasta is cooking and the sauce has started to thicken add the mushrooms and turn the heat up.
You could make dauphinoise potatoes - thinly slice new potatoes and thinly slice a couple of cloves of garlic, chop up and fry a couple of rashers of bacon, get a ceramic baking dish, grease it with butter, put a layer of potatoes in, then bacon, then next layer of potatoes, then some bits of butter then double cream, bake for about 30-40 minutes at 160-180.
This would be much easier if you had more onions. :0