In a large bowl, whisk all beef ingredients except flank steak until well combined. Add steak and stir to make sure each piece is coated in the marinade. Cover and refrigerate overnight.
When ready to cook, pour steak and marinade into a large skillet over medium-high heat. Cook until the steak is cooked through and most of the marinade is gone.
To assemble the bowls:
Put cauliflower in a food processor and pulse until it resembles rice.
Heat olive oil over medium heat in a large skillet. Add cauliflower and cook 3 - 5 minutes, until cauliflower has softened. Divide cauliflower among 4 bowls.
Top each bowl with ¼ of the beef, carrots, cucumber, pickled onion, avocado, and a fried egg. Sprinkle with cilantro and sesame seeds before serving.
To make the sriracha mayo:
Whisk together mayo and sriracha until combined. Serve on the side if desired.