Total Time: 30 minutes1.
Cook pasta in a large pot of boiling, salted water according to package directions. Just before draining, reserve about 1/2 cup (480 ml) of the starchy pasta water.
Drain the pasta, return it to the hot pot, and cover to keep warm.
While the pasta cooks, heat the olive oil in a large skillet over medium heat.
Add the walnuts and garlic, stirring frequently for about 2 minutes until lightly browned and fragrant.
Add the bell peppers and red onion, and cook for 5-7 minutes until crisp-tender, stirring often.
Stir in the tomatoes, parsley, rosemary, and black pepper, and cook for one more minute until the tomatoes are just warmed through.
Pour the walnut-pepper mixture over the cooked pasta in the pot.
Toss gently to combine, adding a splash of the reserved pasta water if needed to create a light sauce.
Serve immediately, topped with a sprinkle of nutritional yeast or vegan Parmesan, if desired.