Place lentils in a large container and cover with several inches of cool water; let soak for 10 to 15 minutes. Drain.
Melt butter in a Dutch oven over medium heat. Add carrots, celery, onion, and garlic; cook and stir until lightly golden brown, 5 to 7 minutes. Stir in paprika, turmeric, salt, red pepper flakes, cinnamon, and pepper. Add lentils and olive oil; cook and stir until lentils are coated with oil, 1 to 2 minutes.
Pour beef broth into the Dutch oven; bring to a boil. Simmer, adding boiling water as lentils absorb the broth to maintain a stew consistency, about 20 minutes. Stir in spinach, lime juice, green onions, and beef bouillon cubes. Continue simmering until lentils are soft, about 1 hour.
Serve stew topped with spoonfuls of yogurt and fresh parsley.