Preheat oven to 425 degrees.
Thaw frozen shredded potatoes in microwave between layers of paper towels to remove moisture.
Place thawed potatoes into a 9” pie plate, drizzle melted butter over potatoes.
Bake potatoes for 25 minutes until browned and edges are crispy. Remove from oven and place on wire rack to cool for 10 minutes.
Prepare corned beef according to package directions. Remove corned beef from pan, set aside
Add 1 tsp. oil to pan then sauté onions and green peppers until onions are translucent.
In a small bowl mix beaten eggs, milk, mustard, salt and pepper.
Spoon corned beef, sautéed onions and peppers into cooled baked hash brown shell.
Pour egg mixture over top then cover with shredded cheese.
Set oven temp to 350°, bake for 25 to 30 minutes or until egg mixture is set. Let stand for 10 minutes before serving.