Soup? Lentil and carrot, spicy bean, squash and chickpea
I've started making vegetable, tomato and queen mince sauce to have with pasta, then either adding a tin of chilli beans to make chilli, or making into a lasagna using home made cheese sauce which is really cheap. I use corn flour and can make it in 5 minutes.
I quite often buy the bags of ready chopped stir fry veg. These a usually £1 in asda and last 2 means for the 3 of us. I usually add a couple of scrambled eggs to the rice, or some cashew nuts to the stir fry. It's also quick to make, so doesn't use much gas.
Our local bakery sells pizza dough at 80p a bag and is enough to make a pizza to serve 3. I mix some tomato purée with some dried herbs and a bit of water, then smear over the rolled and stretched out base. I think bargain mozzarella cheese is 40p a bag from Asda, so you can make home made yummy pizza for £1.50. If there's only 2 of you this should last 2 days.
Have you tried growing some of your own veg from seed? Our tomatoes have done really poorly this year, but our courgettes rhubarb and cabbage have done brilliantly.
Even if you you just grow some mustard and cress or leaves, it can brighten up a sandwich.