Preheat the oven to 375°F. Grease a 9 x 13-inch baking dish.
In a large bowl, stir together mayo, sour cream, cream of chicken soup, Dijon, lemon juice, garlic powder, onion powder, and pepper.
Add chicken, cheddar, celery, onion, and peas (if using). Mix well. Taste and add salt only if needed.
Spread the mixture evenly in the baking dish.
In a bowl, mix crushed chips (or crackers), panko, melted butter, and parmesan (if using).
Sprinkle topping evenly over the casserole.
Bake uncovered 25–30 minutes, until bubbling and golden. Broil 1–2 minutes if desired for extra browning.
Rest 10 minutes, then serve.