Preheat oven to 350 and grease a casserole dish with a little oil.

Add the oil to a Dutch oven or large pot and heat it over medium-high heat. Once hot, add the onions and cook for 3-4 minutes or until soft and translucent.

Add the riced cauliflower to the pot and season with the salt and pepper. Cook for 10-12 minutes or until all of the water has cooked off of the cauliflower, it is starting to get gold and toasty in color, and is nice and soft.

Add the garlic to the pot and cook for 1 minute or until fragrant.

Turn down the heat to medium. Add the milk, garlic powder, Italian seasoning, Dijon mustard, cream cheese, Greek yogurt, and spinach to the pot. Stir until everything is well combined, the cream cheese has melted into the sauce, and spinach has wilted.

Add the chicken and rice into the pot with the cauliflower mixture. Mix together to combine. Pour into the prepared casserole dish and spread out into an even layer in the dish.

Sprinkle the shredded cheddar cheese on top. Cover with foil and bake in the oven for 25 minutes or until cheese is melted and bubbly.

Remove foil and place under the broiler for 2-3 minutes to crisp up the cheese, if desired.