Preheat oven to 375 F
Fill a large pot with water, add 1 tsp of salt and cook the pasta al dente as per the pack instructions. As soon as the pasta reaches al dente stage, use a colander or sieve to drain the pasta then rinse immediately with cold water. Set aside.
Wash all vegetables. To wash the leek, slice it lengthwise down the center of the stalk. Rinse the dirt from between the layers in the center as grit and sand often accumulate there while the plant is growing. When the leek is thoroughly rinsed and all the dirt removed, chop the white and as much of the green part as possible. Prepare the rest of the veggies by cutting to the appropriate size.
Add all the chopped leek, onion, and garlic to a large non-stick pot. Dry (or steam-saute using a small amount of water or broth) for 4-5 mins or until the onions start to brown and go soft. Remove half the mixture and set aside to use with the bechamel. Add the chopped tomatoes, spaghetti sauce garbanzo and cannellini beans, Italian style herb seasonings, and 1 tsp of salt to the pot with the onions and garlic. Bring to a boil. Then, reduce the heat to medium and leave to simmer for 10 mins stirring regularly. Taste and adjust the seasonings and remove from the heat.
Dry or steam saute the peppers, zucchini, eggplant, and mushrooms, and add to the tomato sauce along with the cooked pasta. Mix well and pour into a large casserole dish.