In a large pot or wok, heat oil over medium heat. Add onion and garlic. Saute for 5 minutes or until softened. Add tomatoes and cook until slightly browned.
Add turkey and cook, stirring to crumble until done. Add soy sauce.
Add sweet potatoes to pan and cook on low until soft; about 10 minutes
Remove from heat and squeeze lemon juice over dish. Stir in raisins if using and serve over rice.