Heat oil in a large nonstick skillet over medium heat. Cook onion 3 minutes, until softened. Stir in ginger, garlic, and red pepper flakes; cook 1 minute more. Add tomatoes and coconut milk. Cook 10 minutes or until mixture thickens.
Add shrimp to skillet. Cook 3-4 minutes, until cooked through. Add salt and freshly ground black pepper to taste. Sprinkle with cilantro before serving.