Spiced Apple Walnut Cake with Cream Cheese Icing

Name: Spiced Apple Walnut Cake with Cream Cheese Icing
Cuisine: American
Ingredients: Butter, for greasing the pan; All-purpose flour, for dusting; 3 medium green apples, such as Granny Smith, peeled, cored, and diced into ¼- to ½-inch pieces; 1 1/2 cups pure maple syrup; 3 large eggs, at room temperature; 3/4 cup light brown sugar; 3/4 cup vegetable oil; 1 tablespoon pure vanilla extract; 3 cups all-purpose flour; 1 1/2 teaspoons baking powder; 1 1/2 teaspoons baking soda; 1 tablespoon ground cinnamon; 1/2 teaspoon ground nutmeg; 1/2 teaspoon ground ginger; 1/2 teaspoon fine sea salt; 1 cup chopped walnuts; 1 cup confectioners' sugar; 1/4 cup heavy cream; 4 ounces cream cheese, at room temperature; 3 tablespoons water, plus more as needed; 2 teaspoons pure vanilla extract