Tuscan Burgers

Ingredients
1 1/3lb ground beef
1/3 cup pancetta, rind removed, chopped
1/3 cup basil pesto (90g/3oz)
sea salt, to taste
fresh ground black pepper, to taste
2 small red onions, thickly sliced
2 tablespoons olive oil
3/4 lb rocket or baby spinach leaves
2 small tomatoes, thickly sliced
1/2 cup whole-egg mayonnaise
3-4 bocconcini, sliced
4 italian bread rolls, split
Directions
Place the beef, pancetta and 2 tablespoons of pesto in a processor; season with salt and pepper; pulse until just combined (do not over-process). Form the mixture into 4 patties and chill while you cook the vegetables.
Preheat the oven to 325°F
Heat a chargrill pan or barbecue over a medium heat; toss the onion in a little oil and grill for 1 minute on each side or until just cooked; place the onion in a low oven (200 degrees F) to keep it warm; brush the tomatoes with a little oil and season them with salt and pepper , to taste; then grill the tomatoes for one minute on each side. Place the tomatoes in the oven to keep them warm. Mix the remaining pesto with the mayonnaise.
Brush both sides of the patties with oil. Cook the patties on the chargrill for 2-3 minutes on each side or until they are cooked through. Top the patties with bocconcini and place them in the oven for 1 minute or until the cheese melts. Spread the bread-roll bases with some of the mayonnaise mixture; top with rocket, patties, onion and tomato; drizzle with the remaining mayonnaise mixture and top with the remaining bread-roll halves.