Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
In a large bowl, cream together shortening and brown sugar. Beat in egg and mashed banana, then stir in vanilla. Combine flour, baking soda, salt, cinnamon, and cloves; stir into the banana mixture. Mix in rolled oats and walnuts. Drop by rounded spoonfuls onto prepared cookie sheets. Leave room for spreading.
Bake for 8 to 10 minutes in preheated oven. Allow cookies to cool on cookie sheets for 5 minutes before transferring to a wire rack to cool completely.