To make the flax egg, whisk together the ground flaxseed and water in a small mixing bowl. Set aside for 5 minutes to thicken.
Preheat the oven to 350F. Line a 8 x 8-inch brownie pan with parchment paper.
Add the flour, chocolate chips, baking powder and salt into a big mixing bowl. Mix together well.
In a separate medium mixing bowl, add the brown sugar, oil and vanilla. Whisk to combine. Add the flax eggs and mix again.
Pour the wet ingredients into the dry ingredients. Mix until the batter comes together. It will be thick. Turn the batter out into the brownie pan and press it to the edges; even it out, using a silicone spoonula, a small measuring cup, or a glass.
Bake for 20 to 25 minutes, or until a tester comes out clean. Let the brownies cool in the pan for 10 minutes.
Lift the brownies out by the parchment, place them on a cooling rack and cool completely before cutting into squares. Enjoy!