Preheat oven to 400° F. Cut off thin slice from rounded side of each squash half. Arrange squash, open side down, in roasting pan. Add 3/4 cup water to pan. Cover tightly with foil. Bake until squash is tender about 35 minutes. Remove from oven; discard water. Turn squash open side up. Sprinkle with salt and pepper. Maintain oven temperature.
Meanwhile, cook orzo in pot of boiling salted water until almost tender, about 5 minutes. Drain. Pour milk and broth into same pot; bring to boil. Add orzo; boil until liquid thickens and orzo is tender, stirring frequently, about 5 minutes. Remove from heat. Stir in cheddar and 1 tablespoon Parmesan. Season with hot pepper sauce, salt and pepper.
Divide orzo mixture among squash halves. Sprinkle with 1 tablespoon Parmesan. Bake until tops begin to brown, about 25 minutes.
