Cook the lentils according to the packet instructions. Set aside. * You can also use pre-cooked lentils to save time (they sell them in little pouches in the UK supermarkets).
Preheat the oven to 200C (400F, Gas mark 6).
Place diced sweet potato in a pan, season with salt & pepper, cover with water & bring to a boil. Reduce to a medium heat & cook until the potatoes are soft. When cooked, cool slightly before mashing the potatoes up. Set aside.
In the meantime, fry the onions and garlic in a pan with 1 tbsp olive oil on a low to medium heat until just softened. Add grated carrot & cook for a further 2 minutes. Stir in tomato puree, smoked paprika & chili flakes and cook for a further 2 minutes.
Add cooked lentils into the pan with onions & garlic & mix well. Stir in chopped tomatoes & peas & cook on medium heat for around 5 minutes. Take the pan off the heat, add freshly chopped coriander and season with salt & pepper.
Transfer the lentil mixture into an oven proof dish and spread evenly. Top with sweet potato mash (use a fork to spread the mash evenly).
Bake in the oven for 10-15 minutes until the potato is starting to turn golden brown.