Preheat the oven to 350 degrees. Grease and line an 8x8 baking dish with parchment paper.
In a small bowl, combine 2 tablespoons of flaxseed with 5 tablespoons of warm water. Mix and let stand for at least 5 minutes to thicken.
Meanwhile, in a large bowl, whisk together the dry ingredients: flour, cocoa powder, and salt. Set aside.
Heat a medium saucepan on the stovetop to medium-low heat, pour in the water and sugar. Cook for 5-10 minutes, whisking occasionally. Once the sugar has completely dissolved, remove from heat and immediately pour into the wet ingredients.
Add the oil, flax eggs, and vanilla to the rest of the ingredients. Stir just until combined. Fold in ½ cup of the chocolate chunks/chips.
Pour the batter into the pan and use a spatula to smooth over the top. Try to create an even thickness throughout.
Sprinkle the remaining ¼ cup of chocolate over the top of the brownies, then transfer to the oven. Bake for 35-45 minutes or until a toothpick in the center comes back mostly clean.
Remove from the oven, let cool completely, and carefully lift out the brownies. Slice into 16 squares and enjoy!