Whisk together first 9 ingredients in bowl, set aside. In large skillet or wok, brown turkey with onion in hot oil over medium-high heat 5 minutes, or until turkey is cooked and no longer pink. Add bell pepper. Stir-fry 1 minute longer. Stir in reserved sauce mixture and bring to a boil. Reduce heat to medium; cook and stir 2 minutes to reduce sauce. To serve, spoon about 1/4 cup turkey mixture into lettuce cups and sprinkle with peanuts.