Preheat the oven to 375°F (190°C). Lightly spray a 9×9-inch baking dish with cooking spray.
Pat the chicken breasts dry, season both sides with salt and pepper, and arrange them in a single layer in the prepared baking dish.
In a mixing bowl, stir together the Greek yogurt, Laughing Cow cheese wedges (softened), grated cheddar, steamed broccoli, chopped green onion, onion powder, and a pinch of salt and pepper until well combined.
Divide the broccoli-cheese mixture evenly and spread it over the top of each chicken breast.
Bake uncovered for 20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and is cooked through.
Remove from the oven and let rest a few minutes before serving.