Whisk the chicken stock, soy sauce, cornflour and ginger together in a small bowl; reserve.
Heat oil in a wok or large frypan, add the chicken and garlic stirring continually until chicken is cooked through, 8 to 10 minutes. Stir in mushrooms, water chestnuts and reserved chicken stock mixture. Cook until sauce begins to thicken, 3 to 5 minutes.
Stir snow peas into the pan and cook until tender, 3 to 5 minutes. Transfer to a platter and sprinkle with sesame seeds before serving.