Remove the stalks from the silverbeet and cook in a large pan of boiling salted water for 3 minutes. Drain and set aside.
Season the liver on both sides. Add 2 tbsp olive oil to a non stick frying pan until it's hot but not smoking. Add the sage leaves and liver. Cook for 1 minute on each side. Set aside and keep warm.
Add the rest of the olive oil to the pan with the garlic - cook for 1 minute. Add the silverbeet and cook through with the garlic for a further 2 minutes. Sprinkle lemon juice over the top and serve on individual plates with the liver and sage leaves on top.