1. Preheat oven to 425 degrees F.
2. Bring 1 cup chicken broth to a boil in a medium saucepan; gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork. Place couscous, tomatoes, and the next 6 ingredients in a large bowl. Add 1 tablespoon oil, and season to taste with kosher salt and cracked black pepper; toss to combine. Set aside.
3. Cut 4 (15 x 24-inch) pieces of parchment paper. Fold in half crosswise. Draw a large heart half on each piece, with the fold of the paper being the center of the heart. Cut, following the heart shape, and open. Sprinkle both sides of fillets with 1 TBS of Greek seasoning each. Place 1 fillet near the fold of each piece of parchment. Top each fillet with 1/4 cup onion slices and 3 lemon slices; drizzle 1 teaspoon oil over each serving. Starting at the top of the heart, fold edges of parchment, sealing edges with narrow folds. Twist the end tip to secure tightly. Place packets on a baking sheet. Bake at 425degrees for 12 minutes. Place on plates; cut open. Serve immediately with couscous.