Combine first 6 ingredients in a large zip-top plastic bag; shake well to dissolve salt and sugar. Add pork; seal and refrigerate overnight, turning bag occasionally. Remove pork from bag; discard brine. Pat pork dry with a paper towel. Sprinkle pork with pepper.
Heat a large nonstick grill pan over medium-high heat. Coat the pan with cooking spray. Add pork; cook 3 1/2 minutes on each side or until desired degree of doneness.