With a vegetable peeler, remove zest (colored part of peel) from oranges.
Cut zest into 1-inch-long, thin strips.
In a pan, combine zest and water; simmer, covered, until tender (about 10 minutes); drain and set peel aside.
Ream juice from oranges (you should have about 1 cup).
Place in pan and add sugar.
Boil over medium-high heat, stirring frequently, until sauce is reduced to 3/4 cup (about 15 minutes).
Add orange peel and cook for 3 minutes longer.
Cool; add liqueur, if desired; then cover and chill.
Up to 4 hours before serving, wash, hull, and slice strawberries; gently stir into syrup.
Cover and chill.
Just before serving, cut cantaloupes in half, making a plain or a zigzag edge.
Scoop out and discard seeds.
Evenly spoon strawberries and syrup into the hollow of each melon half.