Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9x5 inch loaf pan with butter or cooking spray, and set it aside.
Mix Dry Ingredients: In a large bowl, whisk together the flour, sugar, baking powder, salt, cinnamon, and orange zest until well combined.
Combine Wet Ingredients: In another bowl, mix the melted butter, egg, milk, orange juice, and vanilla extract until smooth and blended.
Combine Mixtures: Pour the wet mixture into the dry ingredients, and gently fold until just combined. Be careful not to overmix; a few lumps are okay.
Add Cranberries and Nuts: Fold in the cranberries and walnuts (if using) until evenly distributed throughout the batter.
Transfer to Loaf Pan: Pour the batter into the prepared loaf pan. Smooth the top with a spatula, and add a few extra cranberries on top for decoration if desired.
Bake: Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean. If the top is browning too quickly, you can tent it with aluminum foil halfway through the baking time.
Cool: Once baked, remove the bread from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a wire rack to cool completely before slicing.
Serve: Slice the bread and serve warm or at room temperature.