In a small bowl, combine the soy sauce, rice vinegar, sambal oelek, and sweetener until sweetener has dissolved. Set aside.
In a large skillet, heat oil until hot. Add ground turkey, red bell peppers, and onion. Cook, stirring constantly, for 7-10 minutes, until ground turkey is browned.
Pour soy sauce mixture over meat mixture. Turn heat to high and toss meat and sauce and cook 3-5 minutes, until meat is well coated and sizzling. Serve in lettuce cups.