Adapted from http://www.theguardian.com/lifeandstyle/2013/oct/02/jack-monroe-beetroot-feta-lentil-salad-recipe
If you've never heard of Jack Monroe before, I can't recommend her blog A Girl Called Jack enough. She used to feed herself & her son on a budget of £10 a week, and there are lots of frugal recipes to be found within her blog.
200g beetroot, peeled & quartered & then roasted
100g cooked puy lentils
100g feta, crumbled
1-2tbsps balsamic vinegar (optional)
This recipe tastes even better made with vegetables from Community Harvest Whetstone :)