Heat the vegetable oil in a large pan or pot over medium heat.
Add the chopped onion and sauté for about 5 minutes until it becomes translucent.
Stir in the minced garlic and grated ginger, and cook for another 1-2 minutes.
Add the diced red bell pepper and cook for an additional 3-4 minutes until it begins to soften.
Sprinkle the curry powder, ground turmeric, ground cumin, ground coriander, and chili powder over the vegetables. Stir well to coat the vegetables in the spices, and cook for another 1-2 minutes until fragrant.
Add the dried lentils, diced tomatoes (with their juices), and coconut milk to the pot. Stir everything together.
Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for about 20-25 minutes, or until the lentils are tender and the curry has thickened. You may need to add a bit of water if the curry gets too thick.
Season the lentil curry with salt and pepper to taste.