Fill and boil the kettle. Fill a large pot with boiled water, add 1 tsp of salt and cook the pasta as per the pack instructions. Drain and rinse once cooked.
Chopped the peppers, courgette and leek into bite size pieces ensuring to give the leek a good wash in the centre as often soil can hide here. With the leek include the green of the leek too. Peel and chop 1 of the red onions into half moon slices. Add all the veg to 2 baking trays and cover with 1 tbsp of oil per tray and a generous pinch of salt. Bake for 30 mins, giving them a mix once or twice, until the edges of the pepper, onions and leek start to char slightly.
Peel and finely dice the other red onion and the garlic.
Heat a large pot on medium heat, add 1 tbsp of oil and once hot add the chopped onion and garlic. Fry to 4-5 mins until the onions start to brown and go soft. Add the 2 tins of chopped tomatoes along with 1 tsp of salt and 1 tbsp of maple syrup. Bring to the boil and reduce the heat to medium and leave to simmer for 10 mins stirring regularly. Taste and adjust the seasoning and remove from the heat.
In another pot on medium heat add 3 tbsp of oil, once hot sieve in 3 tbsp of white flour and mix together using a whisk. This is called roux and is used to thicken sauces. Cook for 1 minute stirring continuously.
Cook for 1 minute stirring continuously. Add the oat milk slowly and continue to stir continuously. Bring to the boil and allow to thicken. Add a generous pinch of salt and a small pinch of ground black pepper. Remove from the heat. Taste and adjust the seasoning. Add some nutritional yeast if you have some.
Remove the roasted veg from the oven and add to the tomato sauce along with the cooked pasta. Mix well and pour into a large casserole dish. Pour the white sauce / béchamel sauce on top of the pasta, tomato and roasted veg mixture and bake in the oven for 15 mins.