Meanwhile, heat a splash of oil over medium-high heat in a 12-inch skillet; add sausages and cook, turning once, until crisp and brown, 5 to 7 minutes. Remove sausages from skillet, cool slightly, and then cut them into small dice. Return skillet to medium-high heat and add the oil. Add onions and celery; sauté until soft, 8 to 10 minutes. Mix bread, sausages, sautéed onions and celery, raisins, parsley, sage, thyme, fennel, salt, and pepper in a large bowl. Whisk broth and chia seeds; let stand 5 minutes for chia to hydrate. Add to stuffing mixture and toss to coat.