Bring broth and 2 cups water to a simmer in a medium saucepan. Heat oil in another medium saucepan over medium. Add scallion whites and cook, stirring frequently, until translucent, about 2 minutes. Add farro; cook, stirring constantly, until toasted, about 2 minutes. Add wine and cook, stirring, until absorbed.
Add 1/2 cup broth mixture and cook, stirring, until liquid is absorbed. Continue adding broth in this manner, 1/2 cup at a time, until farro is tender but still slightly firm, about 30 minutes. (You may not need all of broth.) Stir in shrimp and peas and cook until shrimp are opaque, 2 to 3 minutes. Remove from heat; stir in cheese, scallion greens, and chopped herbs. Season with salt and pepper. Divide among bowls, top with herb leaves, and serve.