Halve the celery, cut into 8 slices and peel. Boil up plenty of salted water. Cook the celery slices for about 15 minutes, take them out and let them cool down. Cut ham slices into quarters. Cut cheese into 8 slices.
Cut a pocket into each celery slice. Fill with ham and cheese. Beat the eggs in a plate. Turn celery slices first in flour, then in egg and then in sesame seeds. Heat 5 tablespoons of oil in a large pan. Fry the celery cordon bleu on both sides for about 3 minutes until golden brown. Peel and finely dice the onion. Wash and quarter the tomatoes and remove the seeds. Cut tomato quarters into fine cubes. Season vinegar with salt, pepper and sugar, gradually add 3 tablespoons of oil.
Peel and finely dice the onion. Wash and quarter the tomatoes and remove the seeds. Cut tomato quarters into fine cubes. Season vinegar with salt, pepper and sugar, gradually add 3 tablespoons of oil. Add tomato and onion. Clean and wash the lamb's lettuce. Arrange cordon bleu with lamb's lettuce and vinaigrette on plates