*Extra cilantrolime wedges, salt, pepper and reserved coconut milk for serving
Heat oil in a medium-sized saucepan over medium heat. Add onion and cook, stirring often until softened and turning golden, about 8 minutes.
Add garlic, ginger, curry powder and red pepper flakes. Cook about 2 minutes, until fragrant. Add lentils with 2 cups water and cook, stirring continuously, for 1 minute. Add tomatoes, cilantro, salt, pepper and water. Stir.
Set aside 1/4 cup coconut milk for serving and add remaining coconut milk to saucepan.
Bring the mixture to a boil, reduce heat and stirring occasionally, simmer until lentils are soft, but not mushy, 20 - 25 minutes. Season soup with more salt and pepper to taste.
To serve, divide soup into bowls and drizzle with reserved coconut milk and sprinkle additional cilantro on top. Serve with lime wedges.
Soup (without toppings) can be made 3 days ahead. Store covered in refrigerator.