In a bowl, toss the steak with the cornstarch and 1/4 tsp. salt. In a skillet, heat 2 tsp. oil over high. Add the steak; cook until browned, about 5 minutes. Stir in the onion, garlic and red pepper; cook 30 seconds. Transfer steak to a plate. Reduce heat, add the remaining 2 tsp. oil, kale, sugar and 1/4 tsp. salt; cook until kale wilts. Add 1/2 cup water; simmer 5 minutes. Stir in the oyster sauce, soy sauce, water chestnuts and steak; warm through. Serve over rice.