Bring chicken stock to a rolling boil over high heat with a pinch of salt. Remove entirely from heat and add saffron threads, cover and let sit for 5 minutes. Return stock to heat and lower to just boiling, add orzo and cook until pasta is tender yet firm, stirring occasionally to avoid sticking. You might have to add some additional water if necessary. When pasta is al dente, drain immediately and set aside.
In a skillet, heat the olive oil over medium heat. Add garlic, scallions, and tomatoes and saute for about 5 minutes, then add prosciutto last. Continue to saute until prosciutto just starts to crisp up.
Combine orzo with butter, a pinch of pepper, and just a small squeeze of lemon juice. Add the cooked prosciutto, scallion, and tomatoes to the orzo. Check for seasoning and add additional salt if necessary. Serve with freshly grated or shaved pecorino.