Preheat your oven to 200°C and bring a large saucepan of water to the boil with 1/2 tsp salt. Chop the potatoes into 2cm chunks (peel first if you prefer). Thinly slice the mushrooms. Roughly chop the chives. Peel and grate the garlic (or use a garlic press). Drain and rinse the lentils in a sieve. Grate the Cheddar cheese.

Halve any large cauliflower florets, then pop the florets onto a large baking tray. Drizzle with oil, sprinkle over the ground cumin and season with salt and pepper. Toss to coat then spread out in a single layer. When the oven is hot, roast on the top shelf until golden brown and tender, 15-20 mins. Turn halfway through.

While the cauliflower roasts, add the potatoes to the boiling water and cook until you can easily slip a knife through, 15-20 mins.

Meanwhile, heat a drizzle of oil in a large frying pan on medium-high heat. Once hot, add the mushrooms and season with salt and pepper. Cook until browned, 5-6 mins. Add the garlic and harissa paste (add less if you don't like heat) and cook for 1 min. Pour in the water for the sauce (see ingredients for amount), chopped tomatoes, lentils and veg stock powder. Stir to combine then bring to the boil. Reduce the heat to medium and simmer until thickened, 8-10 mins. Once the cauliflower is cooked, stir it through the sauce then remove from the heat. TIP: Add a splash more water if it's a little thick.

Increase the oven temperature to 220°C. Once the potatoes are cooked, drain in a colander and return to the pan, off the heat. Add a knob of butter and a splash of milk (if you have any) and mash until smooth. Season with salt and pepper, then stir in half the chives.

Taste your filling and season if needed, then transfer to an appropriately-sized ovenproof dish (we used 20x20cm for 2 people). Top with an even layer of mash and sprinkle over the cheese. Bake on the top shelf of your oven until golden and bubbling, 10-15 mins. Serve with the remaining chives sprinkled over. Enjoy!