Sprinkle steaks with salt and pepper. In a large nonstick skillet, cook steaks in oil over medium heat for 5-6 minutes on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°).
Meanwhile, combine the clementines, onion and walnuts; set aside. Remove steaks and keep warm.
Add wine or broth to the skillet, stirring to loosen browned bits. Bring to a boil. Reduce heat; simmer, uncovered, for 1-2 minutes or until liquid is reduced to 2 tablespoons. Spoon over steaks. Serve with clementine mixture and rice if desired.