Add the ghee to the pan. When it melts, toss the onion, mushrooms, zucchini, and carrots. Cook, stirring occasionally, until vegetables are just cooked and slightly tender ( you don't want them too soft- I like a little crunch to mine), about 4 minutes. Return the cooked chicken to the skillet and add the toasted sesame seeds. Cook, stirring, for 2 more minutes. Transfer the mixture to a plate and serve with the Magic Mustard Sauce.