Rinse chicken and pat dry with paper towels. Cut each chicken tender in half. Combine lemon juice, lemon peel, thyme, salt, and pepper in a large bowl. Add chicken to lemon mixture; coat well. Marinate 10 minutes. Combine broth and cornstarch in a cup; stir until smooth. Set aside. Heat the wok over medium high heat until hot. Drizzle 1 tablespoon of oil into the wok. Add butter; swirl to coat bottom and heat until hot. Add mushrooms; stir fry 1 minute. Add onion; stir fry 2 minutes. Remove to a large bowl. Heat remaining 2 tablespoons of oil in the wok. Stir fry chicken in single layer 1 1/2 minutes or until chicken is well browned on all sides and no longer pink in the center. Remove to bowl with vegetable mixture. Add corn to the wok and stir fry about 1 minute. Stir cornstarch mixture until smooth; add to the wok and cook until sauce boils and thickens. Add chicken mixture and broccoli to the wok; stir fry until heated through. Serve over hot cooked rice.