Boil the potatoes for 10-15 minutes until tender then refresh in cold water, cool a little and slice.
Toss together the potato slices and tomatoes and divide between 2 serving dishes. Pile the salad leaves on top and set aside.
Coat one side of each salmon fillet with pepper.
Heat a non-stick frying pan or a griddle until hot. Place the salmon pepper-side down and cook for 3-4 minutes, then turn and cook a further 3-4 minutes until just cooked.
Lay the salmon on top of the salad leaves, mix together the orange rind and juice with the mustard, drizzle over the salad and serve.