Preheat the oven to 350 degrees . In a large skillet, crumble the sausage and cook, stirring often, over medium-high heat until browned, about 8 minutes; transfer to a plate. Add the escarole to the skillet, season with salt and pepper and cook until wilted, about 3 minutes. In a 9-by-13-inch baking dish, layer the tomato sauce, ravioli, crumbled sausage, escarole and mozzarella. Bake until bubbling in the middle, about 45 minutes. Let cool for about 10 minutes.