two tins of chopped tomatoes, 1 clove of garlic (crushed), a goodly dollop of any frozen mixed veg, season to taste. Cook the lot until the veg is tender. Delicious. You can blitz it with a processer if you prefer it smooth.
Add gravy powder or granules and you've got beef and veg soup!
Cauliflower and broccoli soup-you can get a bag with both from most supermarkets/freezer shops. Very tasty with a little blue cheese or rosemary. You can also buy bags of mixed swede and carrot-perfect for carrot and coriander soup, or as a start for any mixed veg soup. I've even seen bags of frozen sliced onions. Basically just throw in any veg you like with some stock and one flavour of your choice.