1-First, spray a 9 x 13-inch baking pan with cooking spray and tear the French bread into chunks or cut into cubes, then evenly distribute them in the pan. In a large bowl, whisk together the 6 large eggs and 2 1/2 cups milk. In a separate small bowl, combine the 3/4 cup granulated sugar and 1 teaspoon orange zest; rub them together with your fingers until fragrant, then add this mixture to the eggs and milk, stirring in the 2 tablespoons vanilla extract and 1 teaspoon cinnamon until fully combined. Pour this custard mixture evenly over the bread.

2-Next, in a medium bowl, combine the 1 cup sliced strawberries and 1 cup sliced rhubarb, then pour them evenly over the French toast mixture. Use a spoon to gently press the fruit down into the bread. Cover the pan with plastic wrap and refrigerate for several hours or overnight to let the flavors meld.

3-Now, for the streusel topping, mix the 1/2 cup all-purpose flour, 1/2 cup brown sugar, 1 teaspoon cinnamon, and 1/4 teaspoon salt in another bowl. Add the 1/2 cup cold butter pieces and cut them into the dry ingredients using a fork or your hands until the mixture resembles coarse sand with some pea-sized chunks. Cover and refrigerate this as well. Preheat the oven to 350 degrees F, remove the French toast from the refrigerator, and sprinkle the streusel topping evenly over the top. Bake for 45-55 minutes, or until the dish is set and golden brown. Serve warm with maple syrup for the best flavor.