Heat oil in a saucepan over medium heat. Add onion and celery; cook 6 minutes. Add garlic and flour; cook 2 minutes. Combine stock and half-and-half, and gradually add to saucepan, stirring constantly; bring to a boil. Remove from heat; stir in 1/4 teaspoon salt and 1/4 teaspoon pepper.
Remove from heat, and stir in chicken, parsley, poppy seeds, Worcestershire sauce, 1/4 teaspoon kosher salt, and 1/4 teaspoon black pepper. Scrape the mixture into an 11 x 7-inch glass or ceramic baking dish. Combine breadcrumbs, almonds, and melted butter in a bowl, and toss to combine. Sprinkle breadcrumb mixture over top of casserole, and bake at 350° for 30 minutes.