Place the tuna steaks in a single layer in a non-metallic dish, sprinkle with the garlic, oil and wine, turning to coat evenly. Cover and leave to marinate in the refrigerator for about 30 minutes.
Meanwhile, prepare the crumb topping. Mix together the ciabatta crumbs, pine nuts, chopped basil and parsley, sun-dried tomatoes and lemon zest. Season to taste and put to one side. Make a deep, cross-shaped cut into the base of each tomato and tuck a couple of basil leaves deep into the cuts.
Preheat a cast-iron, ridged grill pan to hot. Lift the tuna steaks from the marinade and place onto the pan. Brush the tomatoes with a little of the marinade and add to the pan. Cook the tuna for about 4 minutes on one side, brushing with the remaining marinade occasionally. Turn carefully, spoon the crumbs on top of the tuna, and sprinkle a few crumbs over the tomatoes. Cook for a further 4 minutes until the tuna is just cooked but still slightly pink inside.
Spread the spinach leaves on a serving platter, arrange the tuna steaks and tomatoes on top and sprinkle with the lemon juice.
3½ portions vegetables
The tuna can be left in its marinade for several hours or overnight in the refrigerator, along with the crumb topping and the basil-filled tomatoes. To make the crumbs, whizz day-old bread briefly in a food processor until crumbs form.