Place the chicken breasts between plastic wrap and gently pound to about 1/2-inch thickness. Rub both sides with olive oil and season with salt and pepper. Heat a nonstick skillet over medium-high heat and cook the chicken until golden and cooked through, about 4–5 minutes per side. Remove from the skillet and let rest while you prepare the vegetables.

Bring a large pot of salted water to a simmer. Add the broccoli florets and cook 2–3 minutes until just tender, then drain thoroughly and set aside. Warm the riced cauliflower according to package directions, then drain in a fine strainer and press with a spatula to remove as much moisture as possible.

Preheat the oven to 350°F (175°C). Dice the rested chicken into bite-sized pieces. In a large bowl combine the drained cauliflower rice, blanched broccoli, diced chicken, sour cream (or cream cheese), garlic powder, Italian seasoning, 1 cup of the shredded cheddar (reserve the remainder), and the Parmesan. Mix thoroughly and taste, adding more salt if needed.

Transfer the mixture to an 8x8-inch baking dish and sprinkle the remaining cheddar over the top. Cover with foil and bake about 25 minutes, until heated through and the broccoli is tender. Remove the foil, switch the oven to broil, and broil 2–3 minutes until the cheese is melted and bubbling. Let cool slightly before serving.