Start by making your caramelised onion base. In a pan over a medium heat fry off the brown onions in a little butter until they are golden and translucent - about 15 minutes.
Add the honey and vinegar and cook out for another 5 until you have a lovely, sticky onion jam-like mixture. Set aside and cool.
Heat the oven to 220ºC/Fan 200ºC/ Gas 6. Unroll the pastry onto a flat baking sheet and, using a sharp knife, score a rectangle 2 finger widths from the edge.
Brush the outer edge with egg wash. Fork the pastry all over the inside of the marked edge.
Scatter the cool caramelised onions, goat’s cheese, oregano and oil right to the edges in the marked box. Bake for approximately 20 minutes or until the tart is completely golden.
Very carefully place your fresh tomatoes row by row in order of the rainbow - red, orange, yellow, green, purple. Drizzle with more oil and honey, and top with thyme, salt and pepper.