Preheat the oven to 350°F. Grease a 9x13-inch baking dish.
Arrange the toasted English muffin halves in a single layer in the prepared baking dish.
In a large bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and onion powder until well combined. Pour the egg mixture evenly over the English muffins.
Sprinkle the crumbled bacon or diced ham evenly over the top, followed by the shredded cheddar cheese and chopped parsley.
Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the eggs are set and the top is golden brown.
Let the casserole cool for 5-10 minutes before serving. Drizzle with hollandaise sauce just before serving.