Spread bread cubes on a rimmed baking sheet and bake until crisped but not golden, about 10 minutes. In a large pan, melt the butter over medium heat. Add the onion, celery, and garlic and cook, stirring frequently, about 7 minutes.
Add the cherry tomatoes, olives, rosemary, and chilli flakes, and cook, stirring, 1 minute. Transfer to a large bowl and season with salt and pepper. Add the parsley, egg and bread; stir to combine. Add the chicken stock, stirring until absorbed.
Season generously with salt and pepper and prepare your bird for stuffing.
