Place lentils, water, cinnamon and garlic in a large saucepan. Bring to the boil, reduce heat and simmer for 15 minutes. Drain well and discard cinnamon stick.
Add carrot, oats and parsley to the bowl of a food processor and pulse until coarse crumbs. Add lentil mixture, egg, spices and seasoning. Pulse until the mixture is smooth.
Remove mixture to a bowl and allow to cool for 10 minutes. Divide into 4 and form into patties. Heat oil in a large frying pan and cook patties for 5-6 minutes each side until golden and crisp.
Meanwhile, combine sour cream, mustard and lemon. Set aside.
Serve patties in buns with greens, cucumber, carrot, beetroot and mint, drizzled with mustard dressing.