Thinly slice the flank steak into bite-size strips, and add to a large bowl. I like to throw my flank steak into the freezer for about 20 minutes before cutting into it. It helps make it easier! Add 1/2 tablespoon of avocado oil, arrowroot, salt, and pepper. Mix thoroughly and set aside.
Heat a very large frying pan over medium high heat for 2 minutes. Add the remaining 2 tablespoons of avocado oil, and let that heat through for another minute. Add flank steak in a single layer, making sure not to overcrowd the pan (it's fine to do this in two batches if you need to.) Cook for about 3 minutes each side until brown and crisping. Remove with tongs or a slotted spoon and transfer to a large plate.
Add bell peppers and white onion to the pan. Sauté over medium heat for about 7 minutes, until soft and tender throughout, stirring occasionally. Add the steak back into the pan, and cook for about 1 minute, stirring frequently. Add coconut aminos and fish sauce and bring to a simmer. Reduce the heat to low, and allow it to simmer for about 3 minutes until it begins to thicken up a bit. Turn off the heat and stir in basil leaves.
Add rice to a bowl or plate, and top off with Thai basil beef. Garnish with fresh cilantro and green onions.