Combine cassava flour, oat flour, ground flaxseeds, and baking powder in a large bowl. Add salt and mix well.
Mix vegan butter into the flour mixture until the mixture is crumbly. You can use your fingers, pastry cutter or food processor.
Next, add the almond milk and shape the mixture into a dough ball. Remember, this is your creation, so feel free to adjust the consistency. If it's too sticky, add extra cassava flour or oat flour. If it's too dry, a little water will do the trick.
Divide the dough into 5-6 balls, place a piece of parchment paper on the counter, and roll out each ball using a rolling pin into about 1/8 inch rounds.
Heat a skillet over medium-high, brush skillet with oil and cook the flatbread until golden brown. Brush the top of the flatbread with oil, flip the bread to the other side, and cook until golden brown, about 2 minutes on each side. Repeat until all the flatbreads are cooked.