In a medium saucepan pour the vegetable oil and place over medium-high heat. Add the onions and fry, stirring frequently for 8 minutes, until soft and caramelized.
Add the curry powder, garlic, ginger and continue to fry for 2 minutes, stirring constantly. Add the lentils, stir through for 1 minute, then add the tomatoes, parsley, water, salt, and a generous number of grinds of pepper.
Pour the coconut milk into a bowl and gently whisk until smooth and creamy. Set aside ¼ cup and add the remaining coconut milk to the soup. Bring to a boil over high heat, then lower to a simmer and cook for 25 minutes or until the lentils are soft but still holding their shape.
Divide amongst four bowls, drizzle with the reserved coconut milk, sprinkle with parsley leaves and serve.