Heat the olive oil in a large pot over medium-high heat until it begins to smoke. Season the beef with salt and pepper, then gently place into the hot oil, and brown on all sides, about 8 minutes. Once browned, remove the beef and set aside, reserving the remaining oil in the pot. Stir in the celery, carrot, onion, garlic, cilantro, and oregano; cook and stir until the onion has softened and turned translucent, about 8 minutes more.
Pour in the chicken broth, tomatoes, and browned beef. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until the meat is beginning to turn tender, about 1 hour.
After the soup has simmered 1 hour, add the lentils, recover, and continue simmering until the lentils are tender, about 40 minutes. Season to taste with salt and pepper, then stir in the parsley. Sprinkle with Parmesan cheese to serve.
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