Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking dish.
Steam or blanch broccoli for 2-3 minutes until just tender, then drain and pat dry.
In a large bowl, combine the cream of mushroom soup, mayonnaise, beaten eggs, 1 cup cheddar cheese, onion, garlic powder, salt, and pepper.
Fold in the broccoli until well coated.
Pour the mixture into the prepared baking dish and spread evenly.
Sprinkle the remaining ½ cup of cheddar cheese on top.
If using, mix the crushed crackers or breadcrumbs with melted butter and sprinkle over the cheese layer.
Bake uncovered for 35-40 minutes, until bubbly and golden on top.
Let rest for 5 minutes before serving.