In a small bowl, add the ground flaxseed and the water. Stir to combine then leave for five minutes to thicken.
In a medium or large heatproof bowl, add the butter and microwave until melted (or mostly melted). Have a microwave plate on the bowl so butter doesn’t sputter out.
Add the oil, sugars, salt and vanilla to the bowl and whisk well to combine. Put the bowl back in the microwave for 30 seconds. Then whisk very well; you'll see the mixture turn thick and shiny.
Whisk in the flaxseed mixture then let the mixture cool for 5 minutes (this is so the heat of the dough doesn't melt the chocolate when it is added.
Add the baking soda, baking powder and flour and switch to a rubber spatula. Stir until mostly combined.
Chop up the chocolate and add it (or use chocolate chips) to the bowl and stir until you cannot see any unmixed flour bits. Cover with plastic wrap to seal and chill for 1-2 hours in the fridge.
Preheat the oven to 350 F. Grease then line a cookie sheet with parchment paper.
Scoop dough mounds onto the prepared pan in 2 tablespoons of dough per cookie. Top with more chocolate if desired.
Bake until the cookies have spread, aren’t wet in the center and have golden edges; this can take around 12 minutes, depending on the size of the cookies.
Out of the oven the cookies will deflate slightly. Once cool, enjoy!