Pat each fish dry with paper towels and sprinkle with salt and pepper, inside andout. Rinse romaine leaves in cold water. Shake off excess water but do not dry leaves. Place 1 leaf on flat surface. Top with 1 lemon slice. Top with onion slice, seperate into rings. Place trout on top. Then repeat lemon/onion layer. Dot with 2 tsp. of butter per fish. Place another romaine leaf on top and tie bundle together with string, wrapping lettuce tightly around fish. Repeat for each fish. Fish can be prepared to this point and then refrigerated but if doing so, cover wrapped fish with a wet towel to maintain moisture. Distribute coals over botom of BBQ or in gas BBQ wet at medium high for 15 minutes, turning bundles once during cooking. Cut string, remove leaves and serve. Yield 6 servings.
Other Notes
Romaine leaves must be as long or longer than the fish after the head is removed. If not, overla using extra leaves. The lettuce keeps the fish moist during the cooking.