Heat the oil in a large skillet over medium-high heat. Add the diced chicken and onions. Season with seasoning salt and pepper, then cook until the chicken is browned and fully cooked and the onions are soft and fragrant.
Stir in the chopped broccoli and cooked rice. If using frozen broccoli, make sure it’s thawed and drained to avoid extra moisture. Mix everything so the ingredients are evenly distributed in the skillet.
Add the cream of mushroom soup and half of the shredded cheddar cheese to the skillet. Stir until the mixture is creamy and fully coated. Everything should be evenly mixed and slightly thick.
Grease your baking dish, then spread the mixture evenly into it. Sprinkle the remaining cheese on top, then finish with a dusting of paprika and parsley for color.
Bake uncovered at 375°F (190°C) for 20–25 minutes, or until the cheese on top is melted, golden, and bubbling around the edges.
Once baked, let the casserole sit for about 5 minutes before serving. This short rest helps it set and makes it easier to scoop neat servings.