In a small bowl, combine all marinade ingredients.
Thinly slice beef against the grain and place in medium bowl. Pour marinade over sliced meat and stir to combine. Cover and refrigerate 4 hours or overnight for best results. Let beef stay at room temp 30 min before cooking.
Heat a large, heavy non-stick pan on high heat. Add meat and sauté without stirring for 2-3 min or until lightly browned. Stir and continue cooking additional 3-5 min, stirring occasionally or until fully cooked, liquid has evaporated, and the sauce has caramelized on the beef.
Heat tortillas on a hot dry skillet or directly on the grates of your gas stove-top, turning frequently.
Stir together all taco sauce ingredients.
To assemble tacos, place meat over toasted tortillas and top with purple cabbage. Add sprigs of cilantro, diced avocado, and drizzle generously with taco sauce.