In a medium pot saute chorizo, in the olive oil over medium heat, seasoned with salt and red chili flakes. Cook until browned and the fat from the chorizo has been rendered. Add the red onion and garlic, and cook until the onion is translucent. Add the clams, chicken stock, white wine, sherry vinegar and steam until open. While the clams are steaming, grill or toast slices of the crusty bread with butter or olive oil until golden. When the clams have opened toss with scallions, and parsley. Pour into a large bowl, and place grilled bread on top for garnish, and dipping.