Place the chicken in a large bowl. Add the shallot, thyme, Worcestershire and Tabasco sauces and egg yolks. Season to taste and mix well.
Heat a griddle pan (or ordinary frying pan). Using your hands, divide the chicken mixture into 4. Shape into patties and cook for 6–10 minutes on each side, depending on the thickness of the patties.
Cut the ciabatta in half horizontally and toast the 2 lengths under a preheated grill. Cut each piece in half. Spread the ciabatta with mustard and mayonnaise. Top with tomato slices and herb salad leaves, finally adding the griddled chicken burgers on top. Garnish with a little chopped thyme, if liked.