1. Preheat your oven to 190°C/Fan 170°C/Gas 5. Fill and boil your kettle, then fill a large pan with the hot water. Top up, if needed, and add a pinch of salt. Cover and bring to the boil.
2. Peel and finely chop the onion. Halve the pepper, scoop out the seeds and membrane, and finely chop it. Put a deep, ovenproof frying pan or shallow casserole dish on a medium heat and add the chopped veg with a splash of olive oil. Season and fry, stirring, for 6-8 mins till glossy.
3. Meanwhile, peel and chop the sweet potatoes. Add them to the pan of boiling water and simmer for 15-20 mins till tender when pierced with a fork.
4. Drain and rinse the lentils. Peel and grate or crush the garlic. Stir the garlic into the veg with 2 tsp ras al hanut and ½-1 tsp harissa paste (it's hot, so use as much or as little as you prefer). Cook and stir for 1 min.
5. Tip the lentils into the pan. Add 1 tbsp honey and the tinned cherry tomatoes. Half-fill the tin with around 200ml water and pour into the pan. Stir, pop on a lid (or use a baking tray) and bring to the boil, then turn the heat down and simmer for 10 mins, stirring often, till the sauce has thickened.
6. Meanwhile, rinse the spinach or chard, trim off any dry ends then finely slice the leaves and stalks. Stir the greens into the lentils and simmer for 2-3 mins to wilt it. Taste and add a pinch of salt or pepper if needed. Take the pan off the heat.
7. The sweet potatoes should be cooked by now. Drain them, tip back into the pan and add a splash of olive oil. Season, then crush with a fork or masher.
8. If your frying pan is ovenproof, top the lentils with the mash. If not, transfer the filling to an ovenproof dish, then top with the mash. Slide into oven and bake for 20 mins till browned and bubbling. Serve in warm bowls.