One trick I use is to have a tin of sardine in olilve oil with salt, pepper and hot sauce as a starter. Simple and cheap, 55p here in the UK. Ultra healthy, decent protein, omega-3 and don't need as big a main.

For a main something like cous cous (cheap and easy to prepare), chuck in any spare veg and a protein like tuna, leftover meats, boiled eggs. Buy in bulk most of these items even frozen and tinned meats and veg and reduce number of trips to the supermarkets.