Put the garlic in a saucepan with 1 tsp olive oil and fry for about 30 seconds until fragrant. Add the tomatoes and bubble fiercely to thicken a little, this should take about 5 minutes. Stir through the basil and spinach and season. Tip into a lined shallow oven tray, lay the fillets on top and put a couple of lemon slices on each fillet. Season well, then grill for 4-5 minutes, or until the fish is opaque and cooked through. Serve with salad or steamed new potatoes.