While the muffins are baking, prepare the blueberry sauce in a small saucepan over medium-high heat. Stir together blueberries, maple syrup, ½ teasspoon cinnamon, and orange zest. Bring to a boil, reduce heat to medium-low and let simmer for 5 min. Add cornstarch and continue to simmer for approx.. 1 min more, until sauce is slightly thickened. Top warm French toast muffins with blueberry sauce and serve right away.