Preheat the oven to 400 degrees then line a 13" pizza pan with parchment paper or nonstick sprayed-foil and set aside. Alternatively, you can use a half sheet pan. Place a half sheet pan on the bottom rack of your oven in case of spillovers (the chicken releases a little bit of liquid during the baking process, but it cooks off by the end).
To a large mixing bowl add the egg, onion powder, garlic powder, dried oregano, salt, and pepper then stir with a fork to combine. Add the mozzarella cheese then stir to combine. Crumble the ground chicken over the top then stir with a fork until the ingredients are well combined.
Scoop the chicken mixture onto the prepared pan then use a spatula to spread it into an 11" circle (spread into a rectangle if using a half sheet pan). Bake for 20-25 minutes or until the chicken is golden brown on top, rotating the pan halfway through. Note: you may see excess liquid when rotating the pan but it will cook off by the end of the baking time. Set the crust aside to cool slightly.
While the crust is cooling, add the lettuce to a medium-sized mixing bowl then add the Caesar salad dressing and toss to coat. Slice the chicken crust into four slices (or more) then top with the dressed Caesar salad, sliced red onion, and parmesan cheese. Serve immediately.