Grate the zest from one of the lemons and squeeze out the juice. Cut another lemon into 8 wedges. Cut the remaining 3 lemons into 12 slices of 5mm (¼in) thickness. Heat the oil in a small saucepan over medium heat. Add the garlic and cook until golden. Whisk in the lemon juice, then remove from the heat.
Coat the grill rack with cooking spray. Preheat the grill to medium. Lightly brush both sides of the fish fillets with the garlic mixture and sprinkle with salt and pepper. Place 3 lemon slices on the grill rack and put a fish fillet on top. Repeat with the remaining lemon slices and fish. Arrange the lemon wedges alongside the fish on the rack. Grill the fish, without turning, for about 6 minutes or until just opaque throughout. Grill the lemon wedges for about 2 minutes on each side or until browned.
Meanwhile, blend the stock and cornflour in a cup until smooth. Whisk this mixture into the remaining garlic mixture together with the sugar and ¼ teaspoon lemon zest. Bring to the boil over medium-high heat and cook for about 1 minute or until the sauce thickens.
Transfer the fish to plates, lemon slices underneath. Spoon the sauce over the fish and sprinkle with the basil and remaining lemon zest. Garnish with the grilled lemon wedges.
*Citrus fruits such as lemon are particularly good for hypertension. They are rich in vitamin C, potassium and pectin as well as providing phytochemicals that may benefit numerous other conditions as well, including allergies, asthma, cancer, cataracts, stroke, heart disease and even the common cold. *Most nutrition experts recommend eating at least 175g (6oz) of fish per week. Fish has more protein, fewer calories and less fat than most meats.