2 tablespoons virgin coconut oil or extra-virgin olive oil
1 medium onion, finely chopped
2 garlic cloves, finely chopped
1 (2 1/2") piece ginger, peeled, finely grated
1 tablespoon medium curry powder (such as S&B)
1/4 teaspoon crushed red pepper flakes
3/4 cup red lentils
1 (14.5-ounce) can crushed tomatoes
1/2 cup finely chopped cilantro, plus leaves with tender stems for serving
Kosher salt, freshly ground pepper
1 (13.5-ounce) can unsweetened coconut milk, shaken well
Lime wedges (for serving)
Heat oil in a medium saucepan over medium. Cook onion, stirring often, until softened and golden brown, 8–10 minutes. Add garlic, ginger, curry powder, and red pepper flakes and cook, stirring, until fragrant, about 2 minutes. Add lentils and cook, stirring, 1 minute. Add tomatoes, ½ cup cilantro, a generous pinch of salt, and 2½ cups water; season with pepper. Set aside ¼ cup coconut milk for serving and add remaining coconut milk to saucepan. Bring mixture to a boil; reduce heat and simmer gently, stirring occasionally, until lentils are soft but not mushy, 20–25 minutes. Season soup with more salt and pepper if needed.
To serve, divide soup among bowls. Drizzle with reserved coconut milk and top with more cilantro. Serve with lime wedges.
Soup (without toppings) can be made 3 days ahead. Let cool; cover and chill.