For the freshest trout, buy direct from the fish farmer. Read more at www.britishtrout.co.uk.
Preheat the oven to 200C/gas 6/fan 180C. Slice half the lemon and stuff the slices, with the sprigs of dill, into the cavity of the trout. Lay the fish on an oiled baking sheet and make 4 diagonal slashes on one side about 4cm long. Drizzle 1 tbsp of olive oil over the fish, season liberally and bake for 15 minutes.
Put the kettle on to boil, then stir the chopped dill into the yogurt with a squeeze of lemon and some salt and pepper, and set aside. Sprinkle salt on the cut side of the garlic clove and rub it on the inside of a small bowl – this is a good way of getting garlic flavour into food without it being too strong. Empty the boiling water from the kettle into a small saucepan, bring to the boil and cook the runner beans for 3-4 minutes until cooked but still slightly crunchy. Drain the beans and toss them in the garlicky bowl with the radishes and remaining oil.
Serve the fish with the warm beans and the yogurt sauce. Trim the remaining lemon into a wedge to squeeze over the trout and the salad.