Heat the olive oil in a large pot over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and ginger, cooking for an additional 1-2 minutes until fragrant.
Add the curry powder, cumin, and turmeric, stirring well to coat the onions and toasting the spices for about 1 minute.
Pour in the diced tomatoes with their juices, vegetable broth, and rinsed lentils. Stir well to combine.
Bring the mixture to a gentle boil, then reduce heat to low. Cover and simmer for about 20 minutes or until the lentils are tender and the mixture has thickened.
Stir in the coconut milk, then let the curry simmer for another 5-10 minutes. Add salt and pepper to taste.
Remove from heat and add lemon juice. Adjust seasoning if needed.