1. Heat oven to 425 degrees with two racks centered. Spray two 12-by-14-inch roasting or jelly-roll pans with cooking spray. In a small bowl, combine ginger, soy sauce, lime juice, olive oil, and pepper. Set aside.

2. Arrange leeks and tomatoes in one pan, and cod (if using fillets, place skin-side down) in the second pan. Brush all liberally with ginger marinade. Sprinkle all with salt and pepper. Cook 10 minutes. Turn vegetables with a spatula for even browning; brush all again with marinade. Continue to cook until cod is opaque throughout, 2 to 4 minutes more. Transfer cod to a serving plate; keep warm. Continue to cook tomatoes and leeks until tender, 10 to 15 minutes. Add spinach to pan; cook just long enough to wilt, about 5 minutes. To serve, arrange spinach on each plate. Add 1 cod fillet; divide tomato-leek mixture evenly between plates. Serve hot.