Lightly grease the inside of a 6-quart oval slow cooker with olive oil or cooking spray. Place the diced onions and minced garlic across the bottom. Arrange the whole chicken breasts on top of the aromatics in an even layer.

In a small bowl, combine poultry seasoning, garlic powder, onion powder, smoked paprika, kosher salt, and black pepper. Generously rub both sides of the chicken with the spice blend.

Pour the chicken broth and heavy cream around the chicken (avoid washing the rub directly off the top). Dot the top with butter cubes and tuck in the bay leaf. Cover with the lid and cook on LOW for 3.5 to 4 hours (or on HIGH for 2 to 2.5 hours) until the chicken reaches an internal temperature of 165°F and shreds effortlessly.

Transfer the cooked chicken to a clean cutting board or bowl and shred into bite-sized rustic pieces using two forks. Discard the bay leaf.

Stir the rinsed, uncooked long-grain white rice directly into the hot, bubbling broth in the slow cooker. Return the shredded chicken to the pot, stirring well to ensure the rice is submerged evenly. Cover tightly and cook on HIGH for 25 to 30 minutes, or until the rice is tender and has absorbed the creamy broth.

Turn off the heat or switch to the WARM setting. Stir in 1.5 cups of the shredded cheddar and all of the grated parmesan until silky and smooth. Sprinkle the remaining 1 cup of cheddar across the top, replace the lid, and let rest for 5 minutes until the cheese is completely melted and bubbly.

Garnish generously with fresh chopped parsley and freshly ground black pepper. Fluff lightly with a serving spoon and spoon warm, hearty portions into dinner bowls.