Place the broccoli in microwave-safe bowl and steam until thawed.
Pour olive oil in skillet on medium-low and add diced onion. Cook for 3 minutes. Turn up heat to medium and add cubed chicken. Season with lemon-pepper, poultry seasoning and 1 teaspoon salt. Cook until chicken is no longer pink.
Mix cream of chicken soup, sour cream, milk and pepper in large bowl. Add the chicken/onion mixture and 1/2 cup of cheese (and stuffing, if using) and stir together. Season with remaining salt, if necessary.
Pour ingredients into 8x8 baking pan, and sprinkle the top with 1/2 Cheddar cheese. Mix the melted butter with the bread crumbs, and sprinkle over the cheese.
Bake in the preheated oven for 25 minutes, or until bubbly and lightly brown.