Combine first 4 ingredients and 1/4 cup water in a small saucepan; let stand 1 minute. Cook over low heat, stirring until gelatin and bouillon cube dissolve. Remove from heat.
Stir in remaining 1 cup water, lemon juice, and hot sauce; chill until mixture is the consistency of unbeaten egg white.
Stir in tomatoes and next 3 ingredients; spoon into 6 lightly oiled 1/2-cup molds. Chill until firm.
Unmold onto a lettuce-lined serving plate; dollop each with mayonnaise, if desired.
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