For the soup: Place a deep soup pot over medium heat and add oil, onion, celery, and carrots. Cook until vegetables are tender — 7 to 10 minutes. Add garlic and stir; add farro, peas, tomatoes and stock, and stir.
Bring to a boil, and then adjust heat so mixture simmers slowly. Cook until farro and peas are tender, at least an hour, adding stock or water as necessary if mixture becomes too thick. Stir in parsley and sage and cook another 5 minutes. Taste and adjust seasoning, then serve with grated Pecorino Romano.