Cook chicken on the stove top in boiling water. Cube or shred as desired.
Cook rice according to directions.
In a large sauce pan, saute the onion in the olive oil until soft and translucent. Add the garlic and cook for about one minute, stirring, until fragrant.
Sprinkle the flour over the onions and stir to combine. Cook over medium heat for one minute.
Slowly whisk in the milk and chicken broth. Cook, stirring constantly with a whisk, and bring the sauce to a simmer over medium. Add the salt and pepper.
Add the chicken and simmering, stirring the sauce frequently, until the sauce has thickened, about 5-8 minutes.
At this point if you want the sauce to thicken more, in a small bowl whisk together 2 Tbsp flour and 2 Tbsp water until smooth, you don't want lumps. It should look like a paste. Drizzle a little of the flour mixture at a time while whisking into to sauce mixture until desired thickness is reached.
Serve over rice.
Chop green onions, celery, carrots, tomato, and green pepper. Add desired toppings to your haystack.