Sprinkle fish with pepper, lemon juice and olive oil. Place under a pre-heated grill and cook for about 3-4 minutes per side. Fish may also be cooked on an outdoor barbeque grill.

Meanwhile, use a sharp knife to shred the spinach finely. Place in a large saucepan and add a pinch of salt. Cover and cook over moderate heat with only the water that clings to the leaves after washing. Cook about 2 minutes, or until leaves are just slightly wilted. Set aside.

Place egg yolks in a food processor, blender or cup of a hand blender. Add the garlic, crushed, if using a hand blender. Process several times to mix eggs and puree garlic. Add salt, pepper, mustard and cayenne pepper. With the machine running, pour oil through the funnel in a thin, steady stream. Follow manufacturer's directions if using a hand blender.

When the sauce becomes very thick, add some lemon juice or vinegar in small quantities.

To serve, place a bed of spinach on a plate and top with the swordfish. Spoon some of the garlic mayonnaise on top of the fish and serve the rest separately.