Heat a large pot over medium heat and add the onion, garlic, and ginger. Cook for 3 minutes until the onion softens.
Stir in the Thai red curry paste and cook for 1 minute to release its aroma.
Add the bruised lemongrass stalks, carrots, and red bell pepper. Cook for 2 minutes, stirring often.
Pour in the diced tomatoes and vegetable broth. Bring the mixture to a simmer.
Add the rinsed lentils and coconut milk. Stir everything together and let it cook uncovered for 25 minutes, stirring occasionally.
Remove the lemongrass stalks. Stir in the lime juice and season with salt and black pepper.
Ladle the stew into bowls and top with chopped cilantro before serving.