This is a very filling vegetarian dish with a delightful variety of colors, textures and flavors. It is from "The One-Dish Vegetarian" cookbook. I prepared it for my husband and his cousin (who is a nutritionist) and they both liked it.
Cook lentils, carrot, and celery leaves in 1 quart water for 15-20 minutes or until lentils are almost tender. Drain the lentils, and reserve the cooking water.
Meanwhile, heat olive oil in large skillet. Add onions and thyme, and sautee for 10-12 minutes.
Add the lentils to the skillet along with 1 cup of the reserved broth. Squeeze excess moisture from the spinach before adding to the skillet. Season with salt and pepper to taste. Simmer over low heat while pasta cooks.
Cook pasta according to package directions. Drain and toss with lentil sauce. Add more lentil broth if too dry. Add parsley and serve with grated Parmesan (or nutritional yeast) if desired.