Preheat the oven to 400 degrees F. Add the ½ lb. brussel sprouts and 2 ½ cup diced carrots to a large baking tray. Drizzle with the 1 tbsp. oil and toss. Season with salt and pepper as desired. Bake for 15 minutes, toss, then bake another 15 minutes until brussel sprouts are tender. Remove the brussel sprouts from the tray if the carrots need another 10 minutes of cooking.
Meanwhile, boil water for the pasta and cook in salted water according to package directions for al dente, then drain.
While the pasta is cooking, heat a large pan on medium heat and add the 3 tbsp. vegan butter and ½ medium chopped onion. Cook for 5 minutes, then add the 1 cup peas and cook another 3 minutes until the onions are tender and the peas are cooked.
Add the cooked pasta, roasted vegetables, 2 tbsp. chopped chives, 3 tbsp. chopped parsley, 1 tsp. garlic powder, 1 tsp. kosher salt, and ½ to ¾ tsp. black pepper. Toss then serve, topping with the (optional) vegan grated parmesan cheese, to taste.