1. In bowl, whisk together orange juice, fish sauce, cornstarch and soya sauce. Stir in beef, tossing to coat. Marinate at room temperature for 30 minutes or refrigerate for up to 1 day. 2. In large non-stick frying pan, heat oil over medium-heat. Cook onion and garlic for 5 minutes or until softened. Add curry paste and cook for 1 minute. Add beef and cook for 2 minutes or until browned but still pink inside. Stir in coconut milk, peanut butter, lime juice and Splenda. Cook, tossing to coat meat with sauce, for another 2 minutes. Garnish with cilantro and peanuts.