Preheat the Oven: Preheat the oven to 400°F so it is ready when the assembled egg bake is placed inside.
Cook the Sausage: Heat 1 tablespoon of oil in a skillet, then add the Italian turkey sausage and diced onion. Cook for about 8–10 minutes, stirring as needed, until the sausage is cooked through and the onion is tender. Add the Vegetables: Add the spinach, sliced cremini mushrooms, chopped basil, salt, and pepper to the skillet.Stir the ingredients together so the seasonings and vegetables are incorporated with the cooked sausage mixture. Prepare the Egg Mixture: Crack the 6 eggs into a mixing bowl and whisk them together with the ½ cup of 1% milk until combined.
Combine the Ingredients: Pour the egg-and-milk mixture into the skillet with the sausage and vegetables, stirring or mixing carefully so the ingredients are evenly distributed.
Prepare the Baking Dish: Butter a 9-by-13-inch baking dish, then transfer the sausage, vegetable, and egg mixture into the prepared dish.
Add the Goat Cheese: Sprinkle the 3 ounces of crumbled goat cheese evenly over the top of the egg mixture.
Bake the Egg Casserole: Place the baking dish in the preheated 400°F oven and bake for about 20 minutes, until the eggs are fluffy and the goat cheese is melted.
Finish and Serve: Remove the baked egg casserole from the oven and, if desired, sprinkle chopped scallions over the top before serving.
