Put at least 1 inch of water in the bottom of a steamer, cover and bring to a boil over high heat. Lay the fish on the steamer's rack, making sure the rack is elevated above the water, and cover again. Steam 4 to 8 minutes, or until the fish is done. (A good-size halibut steak may take 10 or even 12 minutes.) Remove the fish to a warm platter and drizzle with olive oil and lemon juice. Cut into serving portions, sprinkle with coarse salt and serve.