To prepare sauce, combine the first 7 ingredients in a small saucepan; bring to a boil. Cook until reduced to 1/3 cup (about 6 minutes). Cool.
Place the onions, cilantro, peppercorns, garlic, and oil in a food processor; process until finely chopped. Add orange juice mixture, sesame seeds, and 1/2 teaspoon salt; pulse to combine. Set aside.
To prepare steaks, sprinkle the beef with 1/2 teaspoon salt and black pepper. Place steaks on a grill rack coated with cooking spray; grill 3 minutes on each side or until desired degree of doneness. Serve steaks with sauce. Garnish with cilantro sprigs, if desired.