If the puff pastry is frozen, thaw according to the package directions.

Heat the oven to 350˚F / 190°C / gas mark 4. Line a sheet pan with parchment paper and place the bell peppers on it. Slide into the oven. Roast for about 25 minutes, until the skin has burnt spots and the peppers have collapsed and wrinkled. Grab them with tongs, drop them into a brown paper bag, roll the top of the bag closed, and let sit for 10 minutes. This technique makes the peppers easy to peel. Leave the oven on.

Meanwhile, line a plate with a paper towel. Drain the mozzarella and
chop it roughly, then place it on the paper towel to lose moisture. If using fresh oregano, strip the leaves off the sprig and finely chop them. Break 
the egg into a small bowl and lightly whisk it. Peel the peppers, cut them in 
half, and remove the core, filaments, and seeds. Pat them dry and slice 
into strips 1⁄4 inch / 6 mm wide along the ribbing.

Line the sheet pan with fresh parchment paper. Lay the puff pastry sheet on the parchment and prick it in 8 to 10 spots with a fork. Sprinkle the pastry with a pinch of salt and scatter the mozzarella over it, leaving a 1 1⁄2-inch / 4-cm clear border around the edges. Dust the mozzarella with the parmigiano and oregano, then season it with 1 teaspoon salt and the pepper.

Arrange the roasted pepper strips over the tart in whatever pattern you fancy, staying clear of the empty edges. On the day Molly and I shot the tart’s portrait, my fancy was an attempt at a corn stalk. Loosely roll the uncovered pastry edge onto itself until it borders the peppers.

Slide the tart into the oven and set a timer for 30 minutes. When the timer goes off, brush the edges of the tart with the beaten egg and slide it back into the oven. Set the timer for another 15 minutes. When the timer goes off, your tart is done. Let it rest and cool a little before eating.