Heat oil in a large stockpot or Dutch oven over medium heat. Add carrots, celery and onion and cook 5 minutes. Add squash and season with chili powder and ground cumin. Cook 1 minute.
Stir in broth, tomatoes, 1/2 cup water and lentils. Cover and simmer on medium-low heat for 40 minutes, stirring occasionally. Uncover and stir in salt. Simmer, uncovered, an additional 10 minutes. Stir in cilantro and serve.
Fiber-rich butternut squash boasts folate and potassium; heart-protecting carotenoids lend it a bright orange color.