Heat oven to 200C/180C fan/gas 6.
Place the potatoes in a pan of water and
boil for 10-12 mins until tender. Add the
beans for the final 2-3 mins. Drain well
and slice the potatoes in half. Tip into
a roomy baking dish and toss with the
olives, lemon zest and oil. Season well.
Season the fish and wrap with the
pancetta or bacon. Place on top of
the potatoes. Bake for 10-12 mins until
cooked through, then add a squeeze
of lemon juice and scatter with
tarragon before serving.