Put the ginger balls on a board and slice them thinly. Pile up the slices from each ball and cut through them to make thin matchstick strips. Put these in a bowl that's large enough to hold the salmon and add 2tbsp of the stem ginger syrup from the jar. Peel the garlic cloves and slice them thinly, then add them to the bowl with the ginger. Stir in the soy sauce, orange zest, orange juice and red chilli.
Put the salmon in the bowl with marinade. Season with lots of ground black pepper and turn a couple of times, ending with the fish skin side up. Cover and chill for 30 minutes.
Preheat the oven to 220C/Fan 200C/Gas 7. Line a small baking tray with baking parchment. Take the salmon fillets out of the marinade, scraping off any bits and pieces, and place them on the tray, skin side down. Season with more ground black pepper. Bake for 12-15 minutes, depending on the thickness of the salmon.
While the salmon is cooking, prepare the sauce. Pour the marinade into a small non-stick saucepan and bring to the boil. Cook for 6 minutes or until the liquid has reduced and the garlic is softened. You need enough of the marinade to pour over the salmon but not swamp it completely.
Put the salmon fillets on warmed plates, carefully lifting off the skin as you go. Spoon the hot sauce over the salmon and serve with a small portion of rice or new potatoes and some steamed or stir-fried vegetables.