1Whisk the olive oil, juice of 1 lemon, lemon zest, red wine vinegar, 3 cloves of the garlic, the oregano, 1 1/2 tsp of the salt, and the pepper in a large bowl. Add the pork cubes and toss until every piece is coated. Marinate at room temperature for 30 minutes, or in the fridge for up to 8 hours.
2While the pork marinates, make the tzatziki. Stir together the yogurt, grated cucumber, the remaining 2 cloves garlic, the dill, a squeeze of juice from the second lemon, and the remaining 1/2 tsp salt. Chill until serving.
3Toss the tomato wedges and red onion with a squeeze of the remaining lemon juice and a pinch of salt. Set aside.
4Heat the grill to medium-high and oil the grates. Thread the pork onto the soaked skewers, packing the cubes snugly but not crushed.
5Grill the skewers for 10 to 12 minutes, turning every 2 to 3 minutes, until charred in spots and the pork is cooked through, with an internal temperature of 145°F or higher.
6Move the skewers to a plate and rest for 5 minutes. Meanwhile, warm the pita on the grill for about 30 seconds per side, until soft and lightly marked.
7Plate it up: skewers and a warm pita on each plate, a generous scoop of tzatziki, and the tomato and onion salad alongside.