Add more oil to the wok if needed and cook zucchini, carrots, and peppers individually for 3–4 minutes, until they are softened but still crisp. Don’t crowd your veggies, and cook in batches, using more oil if necessary. Remove each veggie from the pan and transfer to a large bowl before adding the next kind. Add more oil if needed and cook mushrooms and scallions together for 5–7 minutes until mushrooms are browned and caramelized. Add bok choy and cook for 2 more minutes. Add back in the other veggies and skip to step 6.