Cook lentils and split peas in a large pot of boiling salted water until very tender, about 35 minutes. Drain.
Heat 1/3 cup oil in heavy large skillet over medium heat. Add onion and garlic and saute until onion is translucent, about 5 minutes.
Add turmeric and cumin and stir 1 minute. Transfer mixture to processor (or bowl for use of immersion blender). Add lentils and split peas, celery leaves, lemon juice, chili powderand remaining 3 tbsps of oil. Process until smooth. Season generously (to taste) with salt and pepper.
Transfer to serving bowl. Can be prepared 1 day ahead. Cover and refrigerate. Bring to room temperature before serving. Serve with pita bread.