Make the Yum Yum sauce: In a bowl whisk together 1 cup mayonnaise, 1 Tablespoon ketchup, 1 Tablespoon rice vinegar, 3/4 teaspoon paprika, 1/8 teaspoon garlic powder, and salt and pepper to taste until smooth. Cover and refrigerate (can be made ahead and stored up to one week).

Cut the 2 lb top sirloin against the grain into bite-size chunks and place them in a bowl. Add 2 Tablespoons sesame oil, 1/2 cup low-sodium soy sauce, 1/2 cup peach juice, 4 cloves minced garlic, and 1 teaspoon fresh minced ginger. Toss to coat, cover, and marinate in the refrigerator for at least 30 minutes or up to several hours.

While the steak marinates, cook enough rice to yield 6 cups hot cooked rice (about 2 cups dry white rice) according to package instructions, or prepare cauliflower rice if using. Keep the rice hot until assembly.

Prep the produce: cut the small broccoli crown into small florets; chop the 2 bell peppers into chunks; chop the 1 red onion into chunks; slice the 1 avocado; chop 1/2 cup fresh basil leaves and 1/2 cup fresh cilantro. Set aside.

Heat a large cast-iron or heavy skillet over high heat until very hot. Remove the steak pieces from the marinade and discard the marinade. (If pieces are wet, pat briefly with paper towels to reduce splatter.)

Add the steak pieces to the hot skillet in a single layer and sear without moving for about 1 minute, then flip and continue searing until all sides are browned and the exterior is seared but the interior is not overcooked (about 2–3 minutes total searing time for bite-size pieces, depending on thickness). Remove the steak to a plate and let rest while you cook the vegetables.

Reduce the skillet heat to medium-high. Add 1/2 cup water to the pan, add the broccoli florets, cover the pan, and steam for 2 minutes. Remove the lid, stir the broccoli, and push it to one side of the pan.

Add 1 Tablespoon olive oil to the empty side of the pan, then add the chopped bell peppers and red onion. Sauté together with the broccoli until the vegetables are tender to your liking (about 4–6 minutes). Season the vegetables with salt and pepper to taste.

Assemble the Yum Yum bowls: divide the 6 cups hot cooked rice among bowls. Top each bowl with a portion of steak, a heaping spoonful of the sautéed vegetables, and avocado slices. Drizzle with Yum Yum sauce and Sriracha if desired, and garnish with the chopped basil and cilantro. Serve immediately.