In a large bowl, add the pork tenderloin, salt, pepper, 1 tbsp of the avocado oil and tapioca flour. Toss to coat.
Heat a nonstick skillet over medium high heat with the remaining 3 tablespoons of avocado oil. When the skillet is hot, spread the pork into a single layer and let cook, undisturbed, until it is crisp and browned on one side, about 3 minutes. Flip pork and continue to cook until crisp on the other side, about 3 more minutes. Using a slotted spoon, transfer the browned pork to a plate and set aside while you prepare the rest of the stir fry.
In the same skillet, add the onion and garlic. Cook, stirring, scraping up any of the brown bit until the onions are tender, about 3 minutes. When the onions are tender, add the pork and any of its juices back to the skillet. Pour the sauce into the skillet and toss until well-combined. Bring stir fry to a simmer and let cook, stirring, allowing the sauce to thicken until the pork is well-coated, about 4 more minutes.
Serve with rice and steamed broccoli. Enjoy!