Preheat the oven to 180C/350F/Gas 4. Place the cider in a small pan with the honey and season with pepper. Bring to the boil and then reduce by half until slightly sticky and syrupy.
Arrange the salmon fillets in a non-stick metallic dish, skin-side up.
Pour over the hot cider mixture and then set aside for 10 minutes to allow the flavours to develop.
Heat a large heatproof frying pan.
Season the flesh side of the salmon fillets and add to the pan flesh side down.
Cook for 2 minutes, brushing the top with some of the remaining cider glaze so that the fish fillets begin to caramelise.
Turn the salmon fillets over and brush with the remaining cider glaze.
Add the lemon halves to the pan, cut side down and then transfer to the oven.
Bake for 6-8 minutes until the salmon is tender and lightly caramelised.
Meanwhile, heat the butter in a pan.
Add the spinach and season to taste.
Sauté for 1 minute until just beginning to wilt, then drizzle over the wine and continue to cook until tender.
To serve, drain any excess liquid from the spinach and divide among warmed serving plates.
Arrange a salmon fillet on each one to serve with a caramelised lemon half on the side to garnish.