Heat oil in a large skillet over medium heat. Add carrots, onion, garlic and celery. Cook 5 minutes or until vegetables are soft. Add lentils and thyme. Continue cooking a few minutes more, stirring until lentils are coated. Add tomatoes to lentil mixture, breaking them up a bit. Add 4 cups broth. Bring mixture to a boil. Reduce heat, cover, and simmer, stirring occasionally. The lentils are done when they start to soften a little. Season with salt and pepper. Serve warm over squash.