Cut your sliced bread into 1/2" chunks and cook in a toaster oven until lightly toasted.
Heat 1 tbsp oil in a large skillet over medium heat. Add the chicken and broccoli florets to the hot skillet along with salt and pepper. Cover and cook for 7 minutes. Remove lid and stir. Add chopped onion, paprika, garlic powder, parsley and stir to combine. Cook for another 7 minutes, covered. When done, veggies will be tender and chicken will be cooked through.
Preheat the oven to 375 degrees.
Assemble the casserole, using a 13"x9" baking dish, add the cooked broccoli and chicken mixture evenly into the bottom of baking dish. Scatter the toasted bread on top along with 3/4 cup cheddar cheese. Lightly mix to combine.
In a small bowl, whisk together egg, milk and chicken broth. Evenly pour on top of the casserole.
In another bowl, mix softened butter with 1/4 cup breadcrumbs and 3/4 cup cheddar cheese. Sprinkle evenly on top the casserole.
Cover the casserole with foil and place in the preheated oven for 15 minutes. Remove foil and bake for 10 more minutes. Remove from the oven and let cool for 5 minutes. Enjoy!