Melt the butter in a large saucepan or medium Dutch oven over medium heat. Add the orzo and cook, stirring occasionally, for 2 minutes to toast it.
Add 3 cups of the broth, the garlic, salt, and several grinds of pepper. Bring to a boil, reduce the heat to medium-low, and cook, stirring occasionally, for 10 minutes, or until the broth is absorbed. Add the peas and cook for another 2 minutes, or until heated through.
Remove from the heat and add the lemon juice and zest, Parmesan, and half the herbs, stirring until the cheese is melted. Season to taste, stirring in more broth as needed to keep the orzo lightly creamy.
Serve topped with the remaining herbs and more cheese, if desired.
