Preheat oven to 400 degrees. Line a baking sheet with aluminum foil and lay out the bacon in strips width-wise. Bake for 14 minutes, or until just crispy. Remove from pan and let drain on paper towels. Reserve 2 Tbsp of the bacon grease in a small frying pan over medium heat, add the green onions, and cook for 3-5 minutes, or until they begin to brown and become fragrant.
In a greased 9-inch, deep dish pie plate, add the potatoes evenly across the bottom of the plate. Add the cheeses on top of the potatoes. Sprinkle the cooked green onions over the cheese.
Crumble the bacon into small chunks, then spread it evenly over the top of the potato, cheese, and onion mixture.
In a medium-sized bowl, whisk together the eggs, milk, salt, and pepper, then carefully pour over the contents of the plate, and gently shake the plate to fully distribute the egg mixture. Cover, then place in the fridge overnight, or for 8 hours.
Preheat oven to 350 degrees. Remove cover from pie plate and place in the oven, bake for 60 minutes, or until the cheese is just starting to brown and the center has set. Remove from oven and allow to sit for a few minutes before slicing.