Cook pasta according to package directions, reserving 1/4 cup pasta cooking water.
Heat a large skillet over medium heat until hot. Add onion and cook, stirring frequently, about 3 minutes or until beginning to stick to pan. Add broth, carrots, celery, garlic and Swiss chard and cook 5 minutes or vegetables are tender. Stir in tomatoes, basil, thyme and red pepper. Bring to a boil.
Reduce heat to low and simmer 5 to 7 minutes or until vegetables are very tender and sauce is thickened. Stir in reserved pasta cooking water and heat through, then stir in pasta. Serve with a sprinkle of nutritional yeast, if using.