In a large pot, cook pasta according to package directions. Reserve 3 cups pasta cooking water. Drain and set aside.
In the same pot, cook broccoli with 1/2 cup of the vegetable broth over medium high heat about 3 minutes. Add the mushrooms, zucchini, squash, bell pepper and onion; cook 5 minutes until crisp but tender, stirring frequently. Remove from heat; add pasta and squash.
In a bowl, whisk the remaining 1 1/2 cups broth, garlic, tahini, nutritional yeast, lemon juice, Dijon, salt and pepper. Add to pasta mixture and toss to combine. Add reserved pasta water a little at a time until creamy. Return to heat. Season with salt and pepper.