While your rice and chicken are being prepared or reheated, set up all your toppings in small bowls for easy assembly. Arrange the drained pineapple tidbits, black olives, diced tomatoes, sliced green onions, thawed peas, chow mein noodles, shredded carrots, and toasted coconut in separate serving bowls. This mise en place approach ensures smooth assembly and lets each person customize their haystack exactly how they like it.
In a medium saucepan over medium heat, combine the cream of chicken soup, sour cream, milk, and garlic powder. Stir frequently until the mixture is smooth and heated through, about 3-4 minutes. The sour cream will blend into the soup base, creating a rich, creamy sauce. Add the cooked chicken to the pan and stir gently until everything is warmed through and well combined, about 2-3 more minutes. I like to taste the sauce at this point and add a little salt and pepper if needed—the soup is salty, but sometimes a pinch more makes all the difference in flavor.
Divide the cooked rice among serving bowls or plates, creating a nest-like base. Ladle the creamy chicken mixture from Step 2 over the rice. Top with the shredded cheddar cheese while the dish is still hot so it slightly melts into the sauce. Let each person add their desired combination of toppings from Step 1, building their perfect haystack. I always let guests choose their own toppings because everyone has different preferences—some love the crunch of chow mein noodles, while others prefer extra pineapple and coconut for sweetness.