Heat your oven before using it: Set the temperature to 350°F (175°C). Put oil on a baking dish that measures 9 by 13 inches.
Make sausage: Cook the breakfast sausage in a pan on medium-high heat until it turns brown. Take out of the pan and place to the side.
Make hash browns: In the same pan, cook the frozen hash browns until they are lightly browned and mostly thawed, for about 8-10 minutes.
Make layers in the casserole dish with the hash browns. Put the sausage on top of the shredded potatoes. Add cheese and green chilis on top.
Prepare the egg mixture: In a big bowl, mix together the eggs, milk, onion powder, garlic powder, salt, and pepper. Mix thoroughly.
Add beaten eggs: Add the beaten eggs on top of the casserole.
Cook in the oven without covering for 35-40 minutes, or until the eggs are fully cooked.
