Make the garlic butter: Combine finely minced garlic and softened butter in a small bowl. Set aside until ready to use.
Make the magic mustard sauce (optional): Place all ingredients in a blender and pulse until all ingredients are broken down and well blended. (Optional: toast the sesame seeds in the oven first).
Heat 2 tablespoons of oil in a large skillet or wok over medium-high heat. Add chicken, 3 tablespoons soy sauce, lemon juice, salt and pepper to the pan. Cook 3-4 minutes without stirring.
Add half of the garlic butter, stir the chicken as the butter melts. Cook for an additional 2-3 minutes without stirring or until chicken is cooked through and no longer pink.
If cooking vegetables in the same pan, transfer chicken to a plate and cover with foil. Otherwise, leave chicken in the pan for serving.
Add another tablespoon of oil to the pan. Add onion, zucchini and mushrooms, and season with salt and pepper. Cook vegetables until fork tender, stirring occasionally; about 3-4 minutes. Add garlic butter during the last minute and stir to coat veggies as it melts.
Serve immediately over rice (optional) with mustard sauce on the side for dipping.
Note - This recipe moves quickly. I recommend preparing everything, including sauces, foil and utensils, before you start to cook.Serve with steamed white or brown rice, or fried rice for a complete meal.Leftovers are great for meal prep and even delicious straight out of the fridge.I did not include the Magic Mustard Sauce in the nutritional guide because it's optional. A serving of the sauce would add around an additional 100 calories per serving.