Preheat the Retigo combi oven to 180C. 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.
Roast for 10 minutes, or until softened and lightly browned.
While the vegetables are roasting, heat the remaining oil in a large saucepan and gently fry the onion for 5 minutes, stirring regularly.
Add the chilli and garlic and cook for a few seconds more. Stir in the tomatoes, dried oregano and vegetable stock and bring to a gentle simmer. Cook for 10 minutes, stirring regularly. Set aside.
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.
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.
Spoon a third of the vegetable mixture over the base of GN container 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.
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.
Bake for 40 minutes at the temperature of 160C, 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.