Meanwhile, in a large 12-inch skillet (or 10x13 shallow baking dish) arrange shrimp snugly in one layer, side by side with only the tails overlapping. Pour the butter mixture over the shrimp. Sprinkle with sea salt and a pinch of pepper. Cut one half of the lemon into 5 thin slices and tuck them among the shrimp. Place skillet in oven and roast for 12-15 minutes, just until the shrimp are firm, pink and cooked through. Remove from oven.
Squeeze the remaining half of the lemon over the shrimp. Serve with hot toasted bread to dip into the garlic butter.