1. In a large bowl, mix flour, oats, granulated sugar, brown sugar, baking powder, baking soda, cinnamon, salt, walnuts, and chocolate chips.
2. In a small bowl, beat buttermilk, eggs, and butter.
3. Stir wet mixture into dry ingredients just until evenly moistened (batter will be lumpy).
4. Scrape into a buttered and floured 9- by 5-inch loaf pan, and bake in a 350º oven until a wooden skewer inseted in the center comes out clean, about 50 minutes.