To prepare raita, combine first 5 ingredients in a small bowl. Cover and chill.
To prepare steak, combine the mustard seeds and next 4 ingredients (through cumin) in a spice or coffee grinder; pulse until coarsely ground. Stir kosher salt into spice mixture. Rub spice mixture over both sides of steak; cover and chill 4 hours.
Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add steak; cook 3 minutes on each side or until desired degree of doneness. Place steak on a platter or cutting board; let stand 5 minutes. Cut steak diagonally across grain into thin slices. Serve with raita. Garnish with parsley, if desired.