To make the teriyaki sauce, in a small bowl whisk together soy sauce, rice vinegar, brown sugar, ginger and garlic. In a separate bowl, combine cornstarch and water and whisk until smooth. Whisk the cornstarch mixture into the tamari mixture, then set aside.
Add ½ tablespoon avocado oil to a wok or large skillet and set over high heat. When the oil is shimmering, add onion and red pepper. Season with salt and pepper. Cook for 3 to 5 minutes, stirring often, until the onion is lightly browned. Add the broccoli and water, then cover pan tightly and steam for 2 to 3 minutes, or until the broccoli is crisp tender.
Using a slotted spoon, remove vegetables from the skillet and set aside. Add remaining oil. Once shimmering, add the steak and season with salt and pepper. Cook, stirring constantly, for 1 to 2 minutes, or until the steak is just cooked through.
Add sauce and reserved vegetables back to the pan and bring to a boil. Reduce heat to a simmer and cook for 2 to 3 minutes, or until the sauce thickens slightly. Serve over white rice.
*Nutrition label is for stir-fry only and does not include rice.