Pre-heat the oven to 220C/200C fan ovens/gas mark 7.
Cut the onion into 6 thick rounds. Any trimmings can be kept in a sandwich bag in the fridge and used within 2 days for sauces etc. Heat a large non-stick frying pan over a medium heat. Add the olive oil and when hot fry the onions for 3-5 minutes each side until golden.
Cut the pastry into 6 circles about 10cm diameter, using a large pastry cutter or by cutting around a small plate. Place onto a baking sheet lined with greaseproof paper and score a small border of about 5mm-1cm around the inside edge of each one either with a knife or smaller cutter. Brush the border with olive oil.
Roughly spread the cheese inside the border of the pastry, scatter with thyme/rosemary leaves, sprinkle with the pecan nuts and top with a slice of golden onion. Season with a little salt and a twist of black pepper. The tarts can be placed in the fridge for a few hours or cooked straight away.
When ready, place the tarts in the pre-heated oven for 12-15 minutes until the pastry is golden (they may need a couple of minutes longer if they are being cooked from the fridge).
Toss the rocket in a little balsamic vinegar and a drizzle of olive oil. Season and place onto 6 plates. Once cooked, sit the tarts onto the plates and serve