Preheat the oven to 375°F and lightly spray a 9x13 baking dish with nonstick spray.
Add the chicken breasts to a large bowl and season with the salt, pepper, and garlic powder. Toss to coat.
Heat the olive oil in a large skillet over high heat. Sear the chicken for about 3–4 minutes per side until lightly golden brown. The chicken does not need to be fully cooked at this stage.
Transfer the chicken to the prepared baking dish.
In a medium bowl, stir together the Caesar dressing, sour cream, softened cream cheese, chicken broth, and garlic until combined.
Stir in the Parmesan cheese, then pour the sauce over the chicken.
Sprinkle the mozzarella cheese evenly over the top.
Bake uncovered for about 30 minutes, or until the chicken is fully cooked through and the cheese is melted and bubbly.
Let the chicken rest for about 5 minutes so the sauce can thicken slightly before serving.
Top with chopped parsley if using, then serve warm.