Coat the diced squash in 1 tbsp of olive oil, and place on a large baking sheet. Sprinkle with salt and pepper, and roast the squash for about 30 minutes until it begins to become brown on the edges. Let squash cool, and reduct the oven temp to 350.
Bring a large pot of salted water to a boil, and cook pasta until al dente, about 2 minutes less than the box recommends. Drain, and set pasta aside.
In another large pot, heat 1 tbsp of olive oil and sauté the onion and garlic for 5 minutes until they become soft. Whisk in the arrowroot powder, nutritional yeast, and almond milk, and miso paste. Whisk for 5 minutes until the mixture begins to thicken. Add in the roasted squash and use an immersion blender to puree into a smooth sauce, adding more almond milk if needed if the sauce is too thick. Taste, and add 1tsp salt and pepper, using more if desired.
Add the pasta into the sauce and stir to coat. Then Add the 2 cups of veggies, if using, to the pasta and the sauce.
Grease a large baking dish, and tip all the pasta/sauce mixture into the dish. Top with breadcrumbs, and add to the oven (uncovered). Bake for 20 minutes until the breadcrumbs begin to brown and the pasta starts to bubble. Serve hot, and cover any leftovers for a few days in the fridge. I put leftovers into small wide-mouth pint mason jars and bring to work for a yummy and filling lunch!