Preheat oven to 350°F and grease an 8x4-inch loaf pan.
In a bowl, combine Gluten Free Muffin Mix, water, mashed bananas, and eggs and mix until well combined. Stir in walnuts, if using.
Transfer batter into the prepared loaf pan and bake until a tester inserted into the center comes out clean, about 50 - 60 minutes. Let cool for 10 minutes before removing from pan.