Combine orange juice, champagne, honey, and orange zest in a small pot. Heat it over medium-high heat until it reaches a boil. Then lower the heat and allow it to simmer until it is reduced to a ¾ cup of liquid, about 20 minutes. Then remove from the stove and allow to cool.
While the Mimosa syrup is simmering, prepare your fruit.
Add the watermelon, cantaloupe, grapes, pineapple, and orange slices to a large bowl. When the syrup has reached room temperature, drizzle it over the fruit. Toss to coat the fruit.
Cover the bowl and refrigerate for at least 2 hours before serving.