In a medium bowl, combine the lemon juice, oil, garlic, ½ teaspoon salt, and ¼ teaspoon pepper. Add the tilapia and toss to coat. Let marinate for 10 minutes.
Meanwhile, cook the couscous according to the package directions. Remove from heat and stir in the parsley and sun-dried tomatoes.
Heat grill to high. Grill the tilapia on an oiled grate until cooked through, 1 to 2 minutes per side. Serve with the couscous and lemon wedges.