Using a large sauté pan or skillet, heat your oil over medium-high heat. After a minute or two, add the onions and sauté for a few minutes until slightly softened. Add in the zucchini, summer squash if using, snap peas, shiitake mushrooms and minced garlic and sauté for a few minutes. Season with salt and pepper and continue sautéing for a few minutes longer until the vegetables are tender but not too soft.
Add in the bell peppers, red cabbage and carrots and sauté for 2 to 3 more minutes. Drizzle in the sesame oil and mix together. Add the cooked linguine noodles into the pan along with the mushroom broth, soy sauce, hoisin sauce and oyster sauce. Toss together for a few minutes, or until the noodles are well coated and heated through. Taste and adjust any ingredients as needed.
Garnish with diced green onions and serve immediately. Enjoy!