Preheat your oven to 350 degrees Fahrenheit and grease a 9x5 inch loaf pan.
In a medium bowl, whisk together the flour, baking soda, salt, and cinnamon.
In a large bowl, beat the oil, sugar, and eggs together until smooth.
Stir the dry ingredients into the wet ingredients until just combined.
Fold in the diced mango and walnuts.
Pour the batter into the prepared pan and bake for 55 to 65 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 15 minutes before transferring to a wire rack.