Heat a large skillet or wok over high heat with 2 tablespoons avocado oil. When the oil is very hot, add chicken in batches, being careful not to overcrowd the skillet, you will likely need to do this in 2-3 batches to allow the chicken to crisp up on all sides and cook evenly. Cook until chicken is cooked through and golden brown, about 2-3 minutes per side. Transfer the cooked chicken to a plate and continue until all chicken is cooked. Set aside.
Add 1 tablespoon of avocado oil to the same skillet. Add the mushrooms, carrots, snow peas, water chestnuts and garlic to the skillet. Sauté, stirring often, until the vegetables are slightly tender, about 3-4 minutes.
Pour sauce over vegetables and add chicken back to the skillet. Toss to incorporate. Cook, stirring, until the sauce has thickened and the chicken is coated in the sauce, about 2 minutes.