Add onion and thyme to drippings; cook over medium-high heat, stirring occasionally, until onion is golden brown. Stir in flour; cook 1 minute, stirring constantly. Stir in broth and milk; heat to boiling. Boil, stirring constantly, until thickened. Stir in carrots, tuna, corn, pasta and mustard; heat to boiling. Fold in bacon. Spoon into ungreased 2-quart casserole.