Whisk all sauce ingredients together (except sesame oil and miso) in a bowl and set aside.
Heat a wide pan or wok over high heat with a drizzle of avocado oil. Add garlic and ginger and saute until fragrant. Brown the beef, breaking it up, until cooked through. Season with the black pepper while cooking. Remove beef and set aside.
Add a little more oil to the hot pan. Saute onion and red bell pepper for 2-3 minutes.
Turn up heat, add cabbage and press down — let it sit 1-2 minutes without stirring to caramelize. Toss and repeat until golden in spots.
Add beef back in, pour sauce over everything, and toss to coat. Cook 1-2 minutes until sauce thickens.
Remove from heat and add white miso. drizzle sesame oil over the top. Toss once more and serve over rice.
