Step 1

Preheat the oven to 200C/180C Fan/Gas Put the peppers, courgette and sweet potato into a large baking tray. Drizzle with 2 tablespoons of the oil, season with salt and pepper and toss together.

Step 2

Roast for 30 minutes, or until softened and lightly browned.

Step 3

While the vegetables are roasting, heat the remaining oil in a large saucepan and gently fry the onion for 5 minutes, stirring regularly.

Step 4

Add the chilli and garlic and cook for a few seconds more. Stir in the tomatoes, Italian seasoning (or dried oregano) and crumbled stock cube. Pour over the water and bring to a gentle simmer. Cook for 10 minutes, stirring regularly. Set aside.

Step 5

For the cheese sauce, put the flour, butter and milk in a large saucepan and place over a medium heat. Whisk constantly with a large metal whisk until the sauce is thickened and smooth. (Use a silicone covered whisk if cooking in a non-stick pan.) Stir in roughly two-thirds of the cheeses and season to taste.

Step 6

Take the vegetables out of the oven and add to the pan with the tomato sauce. Stir in the spinach and cook together for 3 minutes. Season with salt and lots of ground black pepper.

Step 7

Spoon a third of the vegetable mixture over the base of a 2½ –3 litre/4½–5¼ pint ovenproof lasagne dish and cover with a single layer of lasagne. Top with another third of the vegetable mixture (don’t worry if it doesn’t cover evenly) and a second layer of lasagne.

Step 8

Pour over just under half of the cheese sauce and very gently top with the remaining vegetable mixture. Finish with a final layer of lasagne and the rest of the cheese sauce. Sprinkle the reserved cheese over the top.

Step 9

Bake for 35–40 minutes, or until the pasta has softened and the topping is golden brown and bubbling. Stand for 5 minutes before cutting to allow the filling to settle.