In a medium bowl, whisk together mayonnaise, ketchup, melted butter, rice vinegar, garlic powder, paprika, and sugar. Cover and refrigerate for at least 30 minutes.

Heat sesame oil in a large wok or skillet over medium-high heat. Add the diced chicken breast and cook for 5-7 minutes until browned and cooked through.

Add broccoli florets and cherry tomatoes to the skillet. Stir-fry for 3-4 minutes until the broccoli is tender-crisp.

Add the chilled cooked rice and soy sauce to the pan. Stir continuously for 3-5 minutes, ensuring the rice is heated through and slightly toasted.

Remove the skillet from heat. Serve the hot rice alongside the chilled Japanese white sauce.