In a 1-1/2 to 2-quart pan, mix gelatin and sugar. add 2 cups water. Place on high heat; stir often until boiling. Simmer for 5 minutes. add lemon peel and juice; let cool. Pour lemon mixture into a metal pan (9 by 13 in. or 10 in. square); cover and freeze until hard, at least 3 hours or up to 3 days. Let mixture stand at room temperature until you can break it into large chunks with a heavy spoon. With an electric mixer or in a food processor, beat or whirl until sorbet is smooth and slushy. Serve at once, or return to freezer in pan until it is firm enough to scoop, about 2 hours; or wrap airtight and store up to 2 weeks. Serve as suggested, preceding, or spoon into bowls. Makes 1 quart, 8 servings. Per serving: 106 cal. (0.9 percent From Fat); 0 g protein; 0.1 g fat (0 g sat.); 27 g carbo.; 7.5 mg sodium; 0 mg chol. dess 141