For fish, preheat oven to 400°F. Place a rack 1 level above center. Arrange filets skin side down on a nonstick or parchment-lined baking sheet and season with seafood seasoning. Spread an even layer of pesto across each filet, covering the flesh completely. Roast until fish is white, flaky and opaque, 15-18 minutes. For an outdoor grill, soak wooden fish boards in water then arrange 1 filet on each board and top with fish seasoning and pesto. Grill over medium to medium-high heat covered until fish is white and flaky. Squeeze the juice of remaining lemon over cooked fish and serve.
For steak or chicken, place EVOO, garlic, rosemary, scallions and lemon slices in a large plastic food storage bag. Season steaks or chicken with salt and pepper, add to bag and marinate a few hours or up to overnight. Grill on a grill pan or outdoor grill over medium-high heat, 12 minutes for chicken and 8-10 for steak 1-1 1/2-inches thick. Let meat stand a few minutes then slice on an angle for chicken or against grain for steaks. Top with pesto sauce; serve with warm crusty bread alongside.