Preheat the oven to fan 180C/conventional 200C/gas 6. Boil the potatoes for 10 minutes until tender. Meanwhile, whisk the mustard, orange juice and honey together in a bowl to make a marinade. Turn the salmon fillets in the marinade until evenly coated, then set aside. Deseed the peppers and cut into thick strips.
Drain the potatoes and tip into a shallow ovenproof dish or roasting tray with the peppers and sugar snap peas. Drizzle over the oil, salt and pepper, then toss everything together. Put the salmon fillets on top of the vegetables and pour over the marinade. Bake for 20-25 minutes until the salmon is cooked and just starting to brown.