Combine steak and soy sauce and refrigerate while preparing other ingredients. Whisk hoisin sauce, water and red pepper flakes in a bowl. Heat oil over high heat; add steak and cook 1 minute without stirring. Then toss steak in skillet until browned. Remove meat and repeat with snow peas; stirring for 2 minutes. Add in all ingredients and cook until sauce is thickened, about 1 minute.