Preheat oven to 350 degrees and grease a 10x13-inch casserole dish. Heat oil in a sauté pan and brown the turkey sausage and brown. Remove sausage and set aside. Using the same pan, melt butter and slowly cook onions and garlic until soft. Add the spinach and wilt for one minute. Arrange half of the bread cubes in the casserole dish.
Sprinkle half of the spinach, half of the sausage, half of the cheese, and half of the oregano over the bread. Beat together the eggs and half and half and season with salt and pepper. Pour half of the egg mixture over the casserole and repeat steps. Bake for 35 to 40 minutes. Serves 8-10.