Remove raspberries from package and place in 1-quart container.
Microwave at MEDIUM (50%) until raspberries are defrosted, 2 to 4 minutes, turning over every minute and gently breaking apart as soon as possible.
Let stand 5 minutes.
Place peach halves in rectangular baking dish, 12 x 8 inches, or 10-inch square casserole.
Cover with plastic wrap.
Microwave at HIGH (100%) until peaches are heated through, 2 to 6 minutes.
Drain raspberry juice in small bowl.
Blend in cornstarch and lemon peel.
Microwave at MEDIUM-HIGH (70%) until thick and bubbly, 2 to 4 minutes, stirring once or twice during cooking.
Place 2 peach halves in each of 4 small bowls.
Stir raspberries gently into sauce.
Top each bowl of peaches with one-fourth of raspberry mixture.
Top with whipped cream, if desired.