Trim any fat from meat. Cut meat crosswise into ½ inch slices. Place each slice between two pieces of plastic wrap. With the heal of your hand, press each slice until about 1/8 inch thick. Remove plastic wrap.
In a shallow dish combine flour, pepper, and salt. Coat meat with flour mixture, shaking off excess.
In a large skillet heat margarine or butter and oil over medium high heat. Add half of the meat; cook for 3 to 4 minutes or until slightly pink in center, turning once. Remove from skillet, reserving drippings in skillet. Cover and keep warm. Repeat with the remaining meat.
Reduce heat to medium. Add mushrooms, snipped fresh or dried rosemary, and garlic to reserved drippings in skillet. Cook and stir just until mushrooms are tender. Add broth, scraping up any browned bits on bottom. Bring to boiling. Boil gently uncovered, about 5 minutes ore until reduced by half. Stir in Dijon mustard, lemon peel, and lemon juice. Heat through.
Serve the mushroom mixture over the meat. If desired, garnish with lemon wedges and fresh rosemary sprigs.