In a large pot, heat some oil over medium heat. Add the chopped onion and cook until soft and translucent, about 5 minutes.
Add the minced garlic and grated ginger, and cook for another 2 minutes until fragrant.
Stir in the curry powder, turmeric, cumin, coriander, and garam masala. Cook for a minute to toast the spices.
Add the rinsed red lentils, diced tomatoes, and coconut milk to the pot. Stir well to combine.
Bring the mixture to a boil, then reduce the heat to low and simmer for about 20-25 minutes, or until the lentils are tender and the curry has thickened. Stir occasionally to prevent sticking.
Season with salt and pepper to taste.
Serve the red lentil curry over cooked rice or with naan bread. Garnish with fresh cilantro before serving.
Enjoy!