Oatmeal Banana Cookies

Name: Oatmeal Banana Cookies
Ingredients: 1 cup ( 135 g ) all-purpose flour; 1/2 cup ( 78 g ) rolled oats or quick oats; 1 tablespoon ( 15 g ) cornstarch; 1/2 teaspoon baking soda; 1/2 teaspoon baking powder; 1/4 teaspoon cinnamon; 1/8 teaspoon salt; 1 small over-ripe banana (enough to make about 1/4 cup mashed ); 1/2 cup ( 117 g ) unsalted butter , melted; 1 large egg; 1 teaspoon vanilla extract; 1/2 cup ( 100 g ) brown sugar , firmly packed; 1/4 cup ( 55 g ) granulated sugar; 1/2 cup ( 75 g ) walnuts, chopped; 1/2 cup ( 75 g ) chocolate chips