Buy whatever veg is cheapest and then plan meals around that on the hoof. Having a variety of seasoning that can be mixed into different combinations for variety.
Bean chilli and rice (use dried beans as cheaper)
Dahl (lentil and/or chana) and rice
Chole bhature (curries chickpeas with bread)
Seitan & veg noodles (seitan is really cheap and easy to make protein if you use vital wheat gluten)
Soups - using whatever veg is on cheap that week. You can add in diced ham, chicken, etc.
Pick up rotisserie chicken late at night when on offer (I've got them for as little as 50p) and then pick apart and freeze to add into noodles, soups, etc.
Curry and rice using onions, chickpeas and frozen vegetables (peas, carrots, green beans, okra, etc). Buy a packet of curry spice mix from an Asian grocery for about £2 and will last months.
Fajitas - peppers and onions in wraps (season with smoked paprika and garlic).
Moroccan stew - potato, sweet potato, carrots, onions, aubergine, etc. Then protein, I use vegetarian meatballs but could use chickpeas, chicken, beef, etc. Whatever you can get on offer.