Begin by peeling and finely chopping the onion, and mincing the garlic. Grate the carrot and set aside in a bowl. Rinse the red lentils in a sieve under cold running water, then set them aside.
Heat a medium to large frying pan over medium heat, adding a drizzle of vegetable oil. Once heated, stir in the chopped onion, minced garlic, mustard seeds, curry powder, and turmeric. Cook for about 1 minute until fragrant.
Add the rinsed lentils and grated carrot to the pan, cooking for another minute to combine.
Pour in the vegetable stock and coconut milk. Bring the mixture to a boil, then reduce the heat and simmer for 15-20 minutes, stirring occasionally, until the dahl thickens and becomes creamy.