Thaw fish, if frozen; rinse and pat dry with paper towels. Weight salmon. Wrap in cheesecloth. Set aside. Remove the rack from a large poaching pan. Add water, 1/2 of a sliced lemon, bouillon granules, bay leaves, and salt to the pan. Bring to boiling.
Place wrapped fish on the rack of the poaching pan; carefully lower rack into the pan. Place onion, carrots, and celery around fish. Add additional water to half-cover fish. Return to boiling. Reduce heat, then simmer, covered until fish flakes easily with a fork. Allow 6 to 9 minutes for each 1/2 pound of fish. Remove fish, reserving broth; cool fish just until cool enough to handle. Do not chill.
Strain reserved poaching broth through a sieve lined with cheesecloth, reserving 4 cups. In a 1-1/2-quart saucepan bring reserved broth and peppers to boiling. Boil, uncovered, about 25 minutes or until broth is reduced to 2 cups. Cool. Remove peppers; set broth aside.
Remove cheesecloth from fish. Using a sharp knife, carefully peel back and discard skin, except for area around head, if present, and tail. Repeat on the other side. Remove fins. Using a narrow spatula, scrape off dark-colored meat. If head is attached, remove eye. Transfer fish to a large serving tray or platter. Cover and chill thoroughly.
Meanwhile, prepare Quick Hollandaise Sauce (see recipe below). Chill. For aspic, soften gelatin in the reduced broth for 5 minutes. Stir over low heat until gelatin dissolves. Stir in lemon juice. Chill until syrupy.
For fish scales, thinly slice unpeeled cucumber. Place on fish. If head is attached, dip olive in aspic, then place in eye socket.
To glaze fish, spoon a little aspic along the mid-line of the fish, letting it flow downward to coat fish. Chill fish for 15 to 20 minutes or until glaze is set. (Aspic in the saucepan should remain syrupy. If it is too thick, heat briefly over low heat. If it is too thin, place the pan in an ice bath until syrupy.) Repeat coating with aspic and chilling until fish has a smooth, even glaze. Before the final glazing with aspic, arrange fresh dill or parsley along the mid-line of fish from head to tail. Pour remaining aspic into a shallow pan. Chill until set.
To prepare lemon cones, make a cut from the center to the edge of each lemon slice. Overlap ends of each slice to form a cone. Pipe a little of the Quick Hollandaise Sauce into each cone. (If necessary, soften sauce at room temperature before piping.) Place lemon cones around fish; garnish cones with additional dill or parsley. Dice aspic in the pan; spoon around fish on serving tray. Serve remaining sauce with fish. Makes 18 appetizer servings.
Quick Hollandaise Sauce
Place egg yolks in a blender container. Cover and blend about 5 seconds or until mixed. In a medium saucepan heat butter, lemon peel, lemon juice, and a dash white pepper until butter is melted and almost boiling. With blender running at high speed and lid ajar, slowly pour in butter mixture. Blend about 30 seconds or until thick and fluffy. Serve immediately. (To reheat, place sauce in a small saucepan over very low heat. Heat, stirring constantly, until warm. If sauce is too thick, stir in 1 teaspoon to 1 tablespoon water.) Makes 1 1/3 cup.