Preheat the oven to 375 degrees and oil a standard-size muffin tin.
Mix the flour, salt, baking soda, baking powder and chopped nuts.
In a larger bowl, mix the oil, sugar, flax seed-water mixture, mango, and vanilla extract.
Mix in the flour mixture until all the wet ingredients are just moist. Do not overmix. The batter should be lumpy, like pancake batter, rather than smooth.
With a standard-sized ice cream scoop, or with a tablespoon, divide the batter equally among the 12 muffin tins.
Bake for about 17 minutes in a 375-degree oven or until a toothpick inserted in the middle of a muffin comes out almost dry, with a few crumbs sticking to it.
Let cool for a couple of minutes before unmolding.