Coat the bottom and sides of a 7x9-inch or 8x8-inch casserole dish with cooking spray, and set the oven to 350°F. An even coating helps the egg mixture release from the corners when you lift out portions.

Use a toaster to crisp the waffles, or place them on a baking sheet in the warming oven for 2 to 3 minutes, then cut them into bite-size chunks. Look for a dry, lightly crisp surface that will hold up better when the custard reaches it.

Cut the chicken into 1-inch bites, using a 30-second microwave warm-up first only if the frozen pieces resist the knife. The pieces should be manageable to cut without crushing the coating or forcing the blade.

Distribute the waffle chunks across the prepared dish, then scatter the chicken among them. A fairly even mix prevents one serving from holding mostly waffles while another holds mostly chicken.

Beat the eggs, milk, and maple syrup together in a bowl, optionally including a pinch of salt or cinnamon, then pour the mixture across the filled dish. The custard should look evenly blended, without separate streaks of egg white pooling around the waffles.

Bake the casserole at 350°F for 50 to 60 minutes, checking the center as the end of the baking window approaches. The middle should no longer look liquid or jiggle loosely, and the exposed waffle edges should turn golden brown.

Allow the casserole to cool slightly before cutting and serving with extra maple syrup if desired. The brief rest helps the custard hold together so portions lift more neatly from the dish.