On a baking tray place the diced vegetable in a single layer, drizzle with olive oil, garlic, and salt. Roast for 40 minutes.
Make the marinara sauce:
Heat a saucepan over a medium heat.
Add the olive oil and garlic. Sauté for 2 minutes, stirring frequently.
Add the tomatoes, salt, pepper, sugar, and chilli flakes.
Simmer for 10 minutes, stirring occasionally.
Make the white sauce:
In a small saucepan, melt the butter. Stir in flour and cook for 2 minutes.
Slowly stir in the milk, carefully allowing the mixture to absorb.
When all the milk is added, bring the sauce to the boil. Stir in the Dijon mustard and cheese. Simmer gently for 8-10 minutes.
Add the roasted vegetables to the marinara sauce.
Assemble the lasagne in a baking dish, starting with the tomato, lasagne sheets, then white sauce. Repeat twice. Finish with 150g grated cheddar on top.
Bake in the oven for 25 minutes at 200°C / 180°C Fan, until piping hot and crisp.