Lentil and Walnut Burgers

150g dried green lentils (pre-soaked)
375 ml water
2 tbls cider vinegar
1 tbls groundnut or olive oil
1 medium onion, finely minced
4-5 large cloves garlic, minced
About 10 large mushrooms, minced
50g minced walnuts
1 tsp salt
Optional: chopped spinach, 1 tsp mustard powder, fresh black pepper, sunflower seeds.

Place lentils and water in a small saucepan and bring to the boil. Lower the heat and simmer, partially covered for about 30 mins, or until the lentils are soft and the liquid is gone. Transfer to a medium sized bowl, add vinegar, and mash well.
Heat oil in a medium sized frying pan. Add onions and saute for about 5 minutes. Add all the remaining ingredients and saute for about 5-10 minutes or until the vegetables are tender. Add the saute to the lentils and mix well. Chill for about an hour before forming into patties.
Form 4 inch diameter burgers. Fry in a small amount of hot oil on both sides until heated through and crispy on the outside.