Heat the vegetable oil in a large pot over medium heat. Add the onion and cook until it softens, about 5 minutes. Stir in the garlic and ginger, then cook for 1 minute more until fragrant.
Add the Thai red curry paste and stir to coat the vegetables. Cook for another minute to toast the paste lightly.
Add the butternut squash cubes, rinsed lentils, vegetable broth, and salt. Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 25 minutes, stirring once or twice, until the lentils and squash are tender.
Stir in the coconut milk and heat through for 5 minutes without letting the stew boil. Remove from heat. Serve bowls topped with fresh cilantro and a squeeze of lime.