1Preheat oven to 220C /200C fan-forced. Line an oven tray with baking paper. Place sweet potato on tray and drizzle with half of the oil. Bake for 15-20 minutes until tender. Mash in a bowl and set aside.
2Cook lentils in a pan of boiling water for 15-20 minutes until softened. Drain well. Transfer to a large bowl to cool.
3Meanwhile, heat oil in a large frying pan on medium. Cook onion and garlic for 4-5 minutes until softened. Add spices and cook for 1 minute until fragrant. Add spinach, stirring until just wilted. Transfer to bowl with lentils and sweet potato. Mix well and season to taste. Chill until cold. Form into patties and toss in flour to coat. Place on a baking paper-lined tray.
4Heat oil in frying pan on medium-high. Cook patties for 2-3 minutes each side until golden. Drain on paper towel. Serve patties with yoghurt and lemon wedges.
5Tip: Brown lentils are also labelled as green lentils. They are larger than the French lentils.