1. Heat olive oil in a large pot over medium heat. Once hot, add the diced onion and cook for about 5 minutes, stirring often, until soft and translucent.

2. Add the garlic, red pepper flakes, and oregano. Cook for 1 minute more, stirring constantly, until fragrant.

3. Pour in the vegetable broth and add the red lentils. Increase the heat and bring the mixture to a boil. Reduce heat and simmer for 10 minutes, allowing the lentils to start softening.

4. Add the diced tomatoes. Bring to a boil again, then lower the heat and simmer for another 10 minutes, until the lentils are tender and the soup thickens.

5. Remove from heat. Blend the soup using an immersion blender in the pot or transfer in batches to a countertop blender. Blend until smooth or leave slightly chunky, based on preference.

6. Return the soup to the pot (if blended separately), stir in the coconut milk, and reheat gently if needed.

7. Mix in the sugar, then season with salt and pepper to taste. Add the chopped fresh basil just before serving.

8. Serve hot.