Preheat oven to 350°F. Brown sausage until fully cooked and drain on paper towel. Leave any remaining fat in skillet. Add 1 tablespoon of olive oil to skillet on med/high heat. Saute onions, garlic and mushrooms until soft; about 5 minutes. Add spinach. Add salt and pepper to taste. Transfer to a large mixing bowl and let cool. Once cooled, add 1 cup cheese, 1/2 cup Quaker® Oats and cubed bread to mixing bowl; toss to combine. Spread evenly in bottom of lightly greased 8 x 8 pan. Whisk together eggs, half-and-half and milk. Pour over bread mixture, cover and refrigerate 2 hours or overnight. Top with reserved 1/4 cup Gruyere, 2 tablespoons oats and Parmesan. Bake for 35-40 minutes or until top is puffed and golden brown.