Preheat the oven to 180ºC/350ºF
Peel and cut the sweet potatoes and carrots into chunks and place them in a roasting tray in an even layer. Sprinkle a bit of salt and black pepper and drizzle with oil. Toss to coat. Put it in the oven for 40 to 45 minutes, or until cooked and golden.
Peel and finely slice the garlic. Peel the onion and cut in quarters. Cut the celery stalk.
Place a saucepan over a medium-low heat and pour in some oil. Sauté the garlic, onion and celery stalk, until lightly golden.
Add the red lentils to the pan. Stir to coat, then pour in the water and coconut milk. Gently bring it to the boil, then let it come to a simmer. Cook the lentils for about 20 minutes, or until they are completely broken down.
Remove the vegetables from the oven once ready and place them into the pan. Blitz the soup with a stick blender until creamy. Or use a blender.
Squeeze in some lime juice to taste and season if needed.
Pour the soup into a cup and add some feta cheese on top.
In case you find the soup a bit on the sweet side you could add some sambal or chili to taste. Enjoy!