Chop 1 of the yellow peppers and all veggies for the fillings into cubes of roughly the same size (for spring onions and green beans just chop segments of them).
Heat the oil in a pan, then add the cubed vegetables except for the tomatoes. Season with salt and pepper and sauté until soft and caramelized. Once cooked add the cubed tomatoes.
In the mean time roughly chop the remaining yellow pepper, place it into a blender cup, then add milk, corn flour, turmeric, garlic powder and salt. Blend until smooth.
Once the veggies are cooked, transfer into a bowl, top with finely chopped herbs and mix until well distributed.
Filter the yellow sauce through a sieve to remove bits of pepper skin, place it in the same pan you cooked the vegetables add the yellow pepper sauce, and heat it on medium-low heat until it thickens (stirring continuously for about 2 to 3 minutes).
Cook the pasta a couple of minutes less of the time indicated on the package (mine was supposed to cook for 15 and I drained after 13).
Drain the water of the pasta and place it in a bowl with a drizzle of olive oil. Make sure to coat well the pasta with olive oil to prevent it sticking together.
Assembling time! On the bottom of your tray arrange a generous amount of yellow sauce.
Begin stuffing every conchiglione with 2-3 teaspoons of diced vegetables, then arrange the pasta on the sauce layer in the tray.
Use up every conchiglione making sure the filling is facing up, then cover with a generous amount vegan grated cheese.
Bake at 180° C (355°F) for 20 minutes and serve hot. If you prefer, you can turn on the grill mode in the last 2-3 minutes to add some extra crunch on the top.