Heat 1 tablespoon of the oil in a large skillet over medium-high heat. Season the steak with ½ teaspoon each salt and pepper.
Cook the steak to desired doneness, 4 to 6 minutes per side for medium-rare. Let rest before slicing.
Meanwhile, cook the couscous according to the package directions. Transfer to a large bowl.
Wipe out the skillet. Cook the remaining 2 tablespoons of oil, garlic, and pine nuts over medium heat, stirring, until golden, 2 to 3 minutes.
Fold the pine nut mixture into the couscous with the spinach, Feta, lemon juice, and ½ teaspoon each salt and pepper. Serve with the steak.