1. Heat oil in a large skillet over medium heat. Add broccoli rabe and 1 tablespoon water. Cover; cook 8 minutes, until crisp-tender, stirring occasionally. Set aside and keep warm.
2. Meanwhile, sprinkle salt and freshly ground black pepper, both to taste, on steaks. Heat large nonstick skillet coated with cooking spray over medium-high heat until hot. Add steaks; cook 3 minutes per side for medium-rare, or longer for desired doneness. Using a meat thermometer, check that meat has reached an internal temperature of 145º. Transfer steaks to a serving plate; keep warm.
3. Add mushrooms to the skillet. Cover; cook over medium-high heat, 3 minutes. Add port. Simmer, uncovered, 3 minutes, until sauce thickens slightly. Serve mushrooms over steaks; top with thyme. Season broccoli rabe with salt and freshly ground black pepper, both to taste. Serve with steaks.