1. Heat the oven to 180C.
2. Chop the sweet potato into 2inch wedges. Put onto a lined tray. Season well and bake in the oven for 30 minutes.
3. Grate the beetroot and put in a sieve and with the back of a spoon squeeze out as much liquid as you can (or squeeze between your hands)
4. Put the beetroot in a bowl with all of the Merchant Gourmet lentils – mash everything together using the back of a fork or put into a food processor and pulse till a sticky mixture.
5. Add the grated garlic, 1 tsp ground coriander and lemon juice to the bowl mixture. Season well with salt and pepper.
6. Add 2 tbsp of the polenta to the mixture ( the other 2 tbsp will be used later).
7. Divide the mixture into 4 and shape into burgers, squeezing them together gently with your hands so that they hold their shape.
8. Sprinkle the remaining 2 tbsp of polenta onto a board and gently coat each burger
9. Put the burgers onto the same baking tray as the wedges and bake for the remaining 20 minutes.
10. Make the dressing by adding the lemon juice with 2 tbsp olive oil, salt and pepper
11. Serve the burgers in a bun or iceburg lettuce with the potato wedges, pouring the dressing over salad leaves.