Preheat oven to 350°F. In a medium bowl, combine beef, orzo, bread crumbs, the 2 ounces feta cheese, the Parmesan cheese, and thyme.
Cut the top off each sweet pepper; remove stems and seeds. Trim the bottom of each sweet pepper so it can stand upright, but do not cut into the inside of the pepper. Divide beef mixture among peppers. Stand peppers in a 2-quart baking dish; pour broth around them. Cover dish with foil.
Bake for 1 to 1- ¼ hours or until peppers are tender and an instant-read thermometer inserted into the center of the beef mixture registers 160°F. If desired, sprinkle with the 1 tablespoon feta cheese.