In a large pot, heat some oil over medium heat. Add the diced onion and cook until softened, about 5 minutes.

Add the minced garlic and grated ginger to the pot. Cook for another 1-2 minutes until fragrant.

Add the curry powder, turmeric powder, cumin powder, cayenne pepper (if using), and salt to the pot. Stir well to coat the onions, garlic, and ginger with the spices.

Add the rinsed and drained red lentils to the pot. Stir to combine with the spices and onion mixture.

Pour in the coconut milk and tomato paste. Stir well to combine all the ingredients. Bring the mixture to a boil, then reduce the heat to low and cover the pot. Let simmer for about 20 minutes, or until the lentils are tender.