Make green peppercorn and tarragon dressing. Place ingredients in screw-top jar; shake well.
2
Boil, steam or microwave potatoes until just tender, drain.
3
Meanwhile, coat chicken all over in black pepper. Cook chicken on heated oiled grill plate (or grill or barbecue) until browned all over and cooked through, slice thickly.
4
When potatoes are cool enough to handle, slice thickly. Cook potato, in batches, on same heated oiled grill plate until browned both sides.
5
Arrange chicken, potato, tomato and onion slices on serving plates, drizzle with dressing.