Melt butter and sauté chopped onion, celery, and carrot until softened
Add minced garlic and cook until fragrant
Stir in flour, celery salt, onion powder, garlic powder, and rosemary
Pour in chicken stock and milk, stirring to combine
Add heavy cream and whole grain mustard
Fold in frozen peas and shredded chicken
Transfer mixture to a baking dish
Top with gnocchi and drizzle with olive oil
Sprinkle grated parmesan over the top
Bake until golden and bubbly
