Preheat oven to 425°F Place a rack on a large baking sheet. Using a food processor, grind the stuffing cubes into crumbs, then transfer to a small bowl. Douse the stuffing with the stock to soften. (Don't clean out the food processor; set aside.).
Drizzle the oil into a large bowl. Add the turkey, season with salt and pepper. Mix in the moist stuffing crumbs, egg, onion, garlic, poultry seasoning, fennel seeds, and crushed red pepper. Roll the meat into 1-1/2 to 2 inch balls . Arrange on the prepared baking sheet and roast until browned, about 15 minutes.
For the couscous: In a medium saucepan, bring the stock and butter to a boil. Stir in the couscous; season with salt and pepper. Cover the pan, turn off the heat and let stand for 5 minutes. Using the reserved food processor, chop the parsley. Fluff the couscous and stir in the parsley and walnuts.
For the sauce: In a small bowl, combine all of the sauce ingredients. Serve with the meatballs and couscous.