Stir the mayonnaise, soy sauce, rice vinegar, sesame oil, smoked paprika, garlic powder, and water in a small bowl. Add water a teaspoon at a time until the sauce drizzles easily.

Pat the steak cubes dry. Season with half the salt and pepper, then toss with 1 tablespoon soy sauce and 1/2 teaspoon sesame oil.

Heat a large skillet over medium-high heat. Add 1/2 tablespoon avocado oil and the steak in a single layer. Sear for 2 to 3 minutes per side, turning until browned and the thickest pieces reach 135°F for medium-rare or 145°F for medium.

Transfer the steak to a plate and add the butter and garlic to the skillet. Cook for 30 seconds, scraping up the browned bits, then spoon the garlic butter over the steak.

Heat the remaining avocado oil in a second skillet over medium-high heat. Add the zucchini, carrots, and mushrooms. Cook for 4 to 5 minutes until the zucchini is tender-crisp and the mushrooms are browned.

Push the vegetables to one side. Add the beaten eggs and scramble until just set, about 1 minute.

Add the cold brown rice, remaining soy sauce, remaining sesame oil, and remaining salt and pepper. Toss everything together for 3 to 4 minutes, breaking up clumps, until the rice is hot.

Divide the fried rice among four bowls. Arrange the steak over the top, then drizzle with the creamy sesame sauce and finish with sesame seeds and sliced green onion.