Thinly slice the garlic.
Heat the oil in a frying pan and sauté the garlic and a pinch of chilli flakes for 20 seconds.
Add the shiitake and balsamic vinegar. Stir for a minute to lightly caramelize, then add the wine. Gently sauté, under cover, for 5 minutes. Add the spinach and continue to sauté for 3 minutes until the spinach has just wilted.
Put the salmon fillets on top. Season with salt and pepper.
Drizzle with oil and scatter a pinch or two chilli flakes on top.
Put the lid on and steam for about 5-8 minutes, depending on the thickness of the salmon.
Serve with a squeeze of lemon juice.