1. 1. In a bowl, reserve 2 tablespoons each of the tomato, cucumber, pepper, and onion to garnish.
2. 2. In the food processor or blender, purée the remaining ingredients (except the croutons) until smooth, adjusting the seasoning to taste with lemon juice, salt, and cayenne pepper.
3. 3. Cover and chill thoroughly, at least 3 hours but preferably overnight. Adjust the consistency as desired with water. Serve in chilled bowls garnished with the reserved vegetables and croutons.