Season chicken with garlic powder, salt, and pepper. Heat oil in a large skillet over medium-high heat. Add chicken and cook, undisturbed, until browned on one side, about 2 minutes. Flip and continue to cook until lightly browned, about 2 minutes (chicken will not be fully cooked at this point).
Add onion and cook, stirring occasionally, until it begins to soften. Add butter and allow it to melt. Add rice and cook, stirring, until rice is coated and lightly toasted, about 1 minute. Stir in taco seasoning until well combined, about 30 seconds.
Add water and stir well, scraping any browned bits from the bottom of the pan. Bring to a boil. Stir once more and reduce heat to a simmer. Cover and cook until liquid has been absorbed, about 20 minutes.
Warm queso in a microwave-safe bowl, stirring every 30 seconds, until heated through, about 2 minutes. Top chicken and rice with queso and serve immediately with desired toppings.
