Heat the pot over medium heat and add the diced onion. Cook for 3 minutes until it softens.
Stir in the garlic and ginger. Cook for 1 minute until fragrant.
Add the Thai red curry paste and stir for 30 seconds to toast it lightly.
Pour in the vegetable broth, coconut milk, red lentils, and sliced carrots. Add the salt and black pepper.
Bring the mixture to a gentle boil, then reduce heat to low. Cover and simmer for 20 minutes, stirring once or twice.
Turn off the heat. Stir in the lime juice. Taste and adjust salt if needed.
Ladle into bowls and top with the chopped cilantro.