Preheat the oven to 190 C / Gas 5. Line a baking tray with foil and make sure to lift the foil a bit round the sides so the juice can't escape.
Place the trout in the foil, skin side down. Juice one half of the lemon and mix with the honey and mustard then drizzle over the trout and season; set aside for 15 minutes. Cut the other half of the lemon into lemon wedges and set aside as a garnish.
Place the tomatoes on a lightly greased baking tray and set aside. Bring two saucepans of water to the boil over a high heat and add the potatoes to pan one and cook until tender.
Bake the fish in the preheated oven for 20 minutes while the potatoes are cooking. Ten minutes in to cooking add the beans to the second saucepan on the hob. Five minutes before the end of cooking add the tomatoes to the oven and cook until just tender. Drain the potatoes and beans.
When the twenty minutes is up everything should be done and ready. Serve the fish with the beans, potatoes and tomatoes and with a lemon wedge on the side.