Cook bacon in a large skillet over medium heat until browned and crisp. Transfer to a paper towel-lined plate to drain, and pour off all but two tablespoons of the bacon drippings from the pan.

Return the pan to the heat and add the chopped onions. Cook until translucent (about 5-8 minutes), season to taste with salt and pepper, then add the hash brown cubes, garlic powder, and paprika. Sauté over medium heat for 2-3 minutes, tossing frequently. Transfer the potato/onion mixture to a 9x13-inch baking dish and spread evenly.

Add the sliced green onions to the same pan and sauté for 2-3 minutes until soft and fragrant. Remove from heat and reserve.

In a medium bowl, combine the pepper jack and cheddar cheeses until blended, then spread over the potato/onion mixture. Next, spread the cooked green onions evenly over the cheese layer. Then, spread the crumbled bacon on top.

In a separate medium bowl, whisk together eggs, milk, salt, and pepper until well-combined. Pour the egg mixture evenly over the layers. Cover and refrigerate overnight (at least 8 hours).

When ready to bake, preheat the oven to 350°F. Bake uncovered for 40-45 minutes or until the cheese is bubbly and golden brown. Allow to stand for 15 minutes before cutting.