Heat oil in a large saucepan over medium-high heat. Add onion; sauté 5 minutes or until tender. Add ginger and garlic; sauté 2 minutes. Add water and tomatoes. Bring to a boil; reduce heat, and simmer 5 minutes. Stir in sugar, chile paste, and salt. Remove from heat; let stand 5 minutes.
Place one-half of tomato mixture in a blender; process until smooth. Pour pureed tomato mixture into a large bowl. Repeat procedure with remaining tomato mixture. Return pureed mixture to pan. Stir in coconut milk; cook over medium heat 2 minutes or until thoroughly heated. Serve with lime wedges.