The 1946 edition of "The Joy of Cooking" included 69 recipes for gelatin molds. The chilled soup's ingredients are molded into an updated aspic that's cool and crunchy. Use an electric juicer here.
Make bell pepper layer: Feed bell pepper and red tomato through an electric juicer. Pour juice through a fine sieve into a small bowl; discard any solids. Skim foam from surface with a spoon. Stir in hot sauce, 1/4 teaspoon salt, and 1/2 teaspoon lemon juice. Sprinkle 1 envelope gelatin over top. Let stand 5 minutes.
Transfer mixture to a small saucepan. Cook over medium heat, stirring constantly, until gelatin has just dissolved, about 1 1/2 minutes. Let cool slightly. Transfer bell pepper mixture to a 4-cup scalloped gelatin mold. Refrigerate until just set and still sticky, about 20 minutes.
Make gazpacho layer: Process yellow tomato flesh, the cucumber, and scallions in a food processor until almost pureed, about 10 seconds. Transfer vegetable mixture to a large bowl. Finely chop basil; add basil, 1 teaspoon each salt and lemon juice, and the vinegar to bowl; season with salt and pepper. Set aside.
Puree reserved yellow tomato seeds and pulp with the garlic in a food processor. Pour through a very fine sieve into a medium bowl; discard solids.
Sprinkle remaining gelatin over garlic mixture. Let stand 5 minutes. Transfer to a saucepan. Cook over medium heat, stirring constantly, until gelatin has dissolved, about 2 minutes. Stir garlic mixture into the reserved gazpacho.
When bell pepper layer has just set, pour gazpacho layer on top. Refrigerate until set, about 4 hours. Aspic can be refrigerated, loosely covered, up to 1 day.
Run the tip of a paring knife around edge to loosen. Dip mold into a bowl of lukewarm water for several seconds. Pat mold dry, and invert onto a serving plate. Garnish with tomatoes and basil.