To make the sauce, place all of the sauce ingredients in a blender or food processor and run continuously to combine all the ingredients until smooth. Stop to scrape sides down as needed and restart.
Prep steak, bell pepper, broccoli and green onions as noted. "Rice" cauliflower to have it ready.
Heat 1 tbsp of sesame oil over medium-high heat in a large skillet or wok. Add beef and season with a pinch or two of salt and pepper. Cook for 3-4 minutes, stirring to cook on both sides, until the beef is just cooked through. Transfer to a plate.
At the same time, in a separate pan, heat avocado oil over medium heat. Add cauliflower rice and season with salt and pepper. Cook, stirring occasionally, until the rice is just tender, about 4-5 minutes.
Add the beef and sauce mixture to the pan with the veggies and stir until the veggies and beef are evenly coated. Continue to cook for 1-2 minutes, or until the sauce has thickened. Turn heat to low. Taste and season with any salt and/or freshly ground black pepper as desired.
Remove from heat and serve teriyaki beef over cauliflower rice. Top with optional sesame seeds if desired.