Preheat oven to 350.
Spray an 8x8-inch pan with non-stick cooking spray. Arrange potatoes on bottom of dish. Sprinkle with cheese, Canadian bacon and green onions. In a large mixing bowl, combine eggs, milk, garlic powder, salt and pepper and pour over potato mixture.
Bake uncovered for 40 minutes or until center appears set. Let stand 5 minutes before cutting. This casserole can be assembled the night before. Cover and chill uncooked casserole, and increase baking time to 60 minutes.