Take a sheet of heavyweight foil and fold double into a large square.
Place the onion in the centre of the square.
Scatter tomatoes over onions and drizzle the ghee over.
Follow with the garlic and thyme and season to taste.
Fold sides up to form a foil tray.
Place on a baking tray and roast in a preheated oven at 200°C for 15 - 20 minutes or until the onion and tomatoes are tender.
Remove from heat and transfer contents to a salad bowl.
Cut the feta into squares and add to the tomatoes.
Drizzle the balsamic vinegar over and toss lightly to mix.
Serve hot or at room temperature as a salad or side dish.