Preheat the oven to 325 degrees. Grease a 12-cup muffin tin.
Remove the casing from the sausage and crumble into a fry pan. Cook over medium heat until done. Remove the sausage from the pan and drain on paper towels. Turn into a medium bowl. Drain all but 1 tablespoon of fat from the pan. Add the chopped mushrooms and cook until golden and brown, stirring frequently. Add to the cooked sausage. Stir in the scallions or chives and the cheese.
Divide the sausage-mushroom mixture evenly among the prepared muffin cups.
In another bowl, whisk together the eggs and milk. Season to taste with sea salt and fresh pepper. Pour the egg mixture into the muffin pan. Bake until the eggs are set and the tops are just starting to brown. Remove from the oven and let the pan cool on a rack for 5 minutes. Transfer the rack to the top of the pan and flip the pan over to remove the quiches. Turn upright and let cool completely.
Serve warm or at room temperature. To store, wrap each quiche individually or store in a tightly sealed container.
Nutritional analysis per quiche: 90 calories, 9 grams protein, 3 grams carbohydrates, 5 grams fat, (0 grams trans fat), 217 mg. sodium, less than 1 gram fiber.