Turn the oven on to 180°C.
Cut the tomatoes in half, then place them in a large baking tray, cut-side facing upwards.
Peel and cut the onion into 6 wedges and arrange them around the tomatoes.
Drain the sardines. Mix 2 tbsp of the sardines oil, garlic and balsamic vinegar. Drizzle it over the tomatoes, then bake for 25 minutes.
Meanwhile, cook the pasta according to the packet instruction and drain. Keep the cooking water and steam your chosen green vegetables over it. Drain and keep warm in the sauce pan.
When the tomatoes are cooked, add the sardines, olives and steamed greens. Toss well then put it back in the oven for 5 minutes to warm through (you can turn off the oven now).
Serve warm over the pasta, with grated Parmesan cheese, if liked.