Combine cantaloupe, sweetener, and lemon juice in a blender or food processor; process until smooth. Transfer mixture to a medium bowl.
Sprinkle gelatin over cold water in a small saucepan; let stand 1 minute. Cook over low heat, stirring until gelatin dissolves, about 4 minutes. Add to cantaloupe mixture, stirring well. Add yogurt, stirring until smooth.
Pour mixture into an 8-inch square pan; freeze until almost firm.
Transfer mixture to a large bowl; beat with a mixer at high speed until fluffy. Spoon mixture back into pan; freeze until firm.
Scoop into 5 individual serving dishes to serve. Garnish each serving with a cantaloupe wedge, if desired (cantaloupe wedge not included in analysis).