Heat oven to 400ºF. Cook hash browns according to package directions until crisp and golden brown; season with salt and pepper.
Place the mushrooms, top side down, on aluminum foil-lined baking sheet. Drizzle olive oil equally over mushrooms and season with salt.
Evenly sprinkle cheese over each mushroom. Divide crispy hash browns into sixths and place on top of each mushroom.
Slice smoked sausage in half lengthwise; cut each half into 1/2-inch thick slices. Arrange sausage slices on top of each mushroom.
Bake at 400ºF. for 15 minutes until heated through. Garnish with chives before serving.