Cut bread into 3/4 inch cubes, spread on a baking sheet, and let sit at room temperature for 30 minutes to dry slightly.

Drain the can of pineapple chunks through a strainer, reserving 3/4 cup of the juice and setting the pineapple aside.

In a large bowl, whisk together 3 large eggs, 1/2 cup whole milk, 3/4 cup reserved pineapple juice, 1 teaspoon vanilla extract, 1/2 teaspoon salt, and 1/4 teaspoon ground cinnamon until smooth.

Add the dried bread cubes and drained pineapple chunks to the custard mixture and stir gently until evenly coated.

Preheat the oven to 350°F (175°C) and grease a 9 by 13 inch baking dish.

Pour the bread and pineapple mixture into the prepared baking dish, spread evenly, and let rest for 5 minutes.

In a medium bowl, combine 1 cup panko breadcrumbs and 1/4 cup granulated sugar. Rub in 1/2 cup cubed butter with your fingers until the mixture resembles coarse sand.

Evenly sprinkle the breadcrumb topping over the casserole without packing it down to maintain light, crispy texture.

Bake for 35 to 40 minutes until the top is deep golden brown and a knife inserted in the center comes out with a few moist crumbs.