Get the lentils ready first. Tip them into a small saucepan, cover with water and add the garlic and sage. Simmer gently for 15-20 minutes until tender. Drain, discard garlic and sage, season with salt and pepper. Stir in olive oil and set aside.
Squeeze the juice of one lemon over anchovies in a bowl, add freshly ground black pepper and drizzle with olive oil. Mix capers with the parsley in another bowl. You can get to here several hours in advance.
Preheat griddle pan until very hot. Season salmon on both sides, then sear, skin-side down (if pan is very hot the skin won’t stick – this goes for grilling on a barbecue, too). Turn fish over when you see it change colour halfway, then sear the other side. This will take 2-3 minutes on each side for rare salmon, but cooking time may vary if pieces of fish are very thick.
To serve, reheat the lentils and put a large spoonful in the centre of warmed plates. Top with the salmon, skin-side up, then scatter the anchovies, capers and parsley on top. Serve with the remaining lemons.