Wash the lettuce, shake dry and cut into bite-sized pieces and place in a bowl. Trim the stalks, base and coarse outer leaves from the fennel, cut downward into thin slices, and then cut into strips. Add these to the salad bowl with the cucumber, radishes, celery, pepper and scallions. Cut the tomatoes into eighths. When ready to serve sprinkle the salad with salt, pepper, oil and vinegar and toss lightly.