In a medium skillet cook sausages in oil over moderate heat, turning them until browned on all sides and cooked through, about 8 minutes, and transfer to paper towels to drain.
In fat remaining in skillet cook onions and garlic, stirring until golden, and stir in herbs (including bay leaf), scallions or parsley, tomatoes with juice, and salt and pepper to taste. Boil mixture, stirring, 5 minutes. Cut sausage into 1/4-inch thick slices. Add sausage and beans to tomato mixture and cook, stirring, until heated through. Discard bay leaf and keep "cassoulet" warm, covered.
In a small skillet heat oil over moderately high heat until hot but not smoking and saute bread until pale golden. Stir in garlic, parsley, and salt and pepper to taste and saute, stirring 1 minute.
Transfer "cassoulet" to a 1-quart serving dish and cover evenly with topping.