Place chicken breasts on a plate. Add salt, crushed peppercorns, 1 tablespoon Worcestershire sauce, 1 tablespoon Dijon mustard sauce and chilli flakes and rub in well. Set aside to marinate for 10-15 minutes.
Heat a non-stick grill pan.
Slit buns and spread some butter over the base half and the top half. Place them on hot grill pan and cook till grill marks appear on both sides.
Heat olive oil in the same non-stick grill pan. Place marinated chicken and cook from both sides till done.
Take tomato in a bowl. Sprinkle salt and crushed peppercorns over them. Halve the slices.
Spread a little Dijon mustard sauce over grilled buns. Spread some guacamole on the bottom half and then place torn lollorosso leaves over it.
Slice the grilled chicken and put into a bowl. Add mayonnaise, Dijon mustard and remaining Worcestershire sauce and mix well.
Put tomato slices over the lettuce and top with the chicken mixture. Spread some guacamole over the chicken. Top with alfalfa and cheese slices. Cover with the top half of the buns and serve immediately.