Spray a large saucepan with nonstick spray. Add onions and garlic. Cook over medium heat until tender, about 5 minutes. Add broth, potatoes, carrots, and beans. Bring to a boil. Reduce heat to medium-low. Partially cover and simmer for 12 minutes. The potatoes should be slightly undercooked. Remove from heat. In a small bowl, stir together mushroom soup and flour. Add to vegetables, along with chicken, parsley, basil, thyme, and pepper. Stir well. Pour into a medium casserole dish. To prepare crust, combine flour, baking powder, sage, and salt in a large bowl. using a pastry blender, cut in butter or margarine until mixture resembles coarse crumbs. Stir in milk. Form a ball with the dough. Add a bit more flour if dough is too sticky. Roll out on a floured surface to fit top of casserole. Place dough over chicken mixture. Prick several times with a fork. Bake at 400 degrees F for 25 minutes, until crust is golden brown. Let cool for 5 minutes before serving.