For the toast: In a medium bowl, whisk the eggs, milk, orange zest, and cinnamon together until smooth. Pour the mixture into a 9-by-13-inch casserole. Add the bread slices in a single layer. Let the bread soak for 10 minutes, turning once.
For the syrup: Peel the orange and remove the white pith. Using a paring knife, cut along the membrane on both sides of each segment. Free the segments and place in a small saucepan. Add the sugar, water, orange liqueur or orange juice, if using, star anise, and cinnamon stick. Bring the mixture to a boil over medium-high heat, stirring constantly, until the sugar has dissolved. Simmer for 5 minutes. Remove the pan from the heat and allow the syrup to cool, about 20 minutes. Remove the star anise pods and cinnamon stick and discard.
Preheat a griddle or large nonstick skillet over medium-low heat and add the butter. Using a spatula, remove the bread slices from the egg mixture, allowing any excess liquid to drain. Cook until golden, about 3 minutes each side. Place on 4 serving plates and drizzle with the orange syrup and orange segments. In a small bowl, toss the blueberries and mint together and spoon on top of the French toast. Dust with powdered sugar and serve.