1-Pickle red onion: Pickle red onion. Place red onion in a large mixing bowl and add red wine vinegar and 1/2 tsp. kosher salt. Let sit while you prepare remainder of the recipe (or at least 15 minutes – tossing occasionally.)
2-Prepare honey-harissa glaze: Prepare honey-harissa glaze. In a small bowl, combine harissa, honey, and fresh lemon juice; stir well to combine. Set aside.
3-Prepare halloumi: Prepare halloumi. Slice halloumi crosswise into 1/3-inch-thick pieces and pat dry with a paper towel.
4-Cook halloumi: Cook halloumi. Heat 1 Tbsp. olive oil in a large skillet over medium-high. Arrange halloumi slices in pan and cook 1 to 2 minutes, until golden brown. Flip and cook 1 more minute. Add honey-harissa glaze and cook 1 minute longer, flipping the halloumi again to coat both sides. Transfer halloumi to a plate and add a pinch of flaky salt, if desired.
5-Mix cucumber-tomato salad: Mix cucumber-tomato salad. To the bowl of red onions, add cucumbers, tomatoes, dill, garlic, and remaining 2 Tbsp. olive oil; toss to combine. Season with an extra pinch of salt (if needed) and a few grinds of black pepper.
6-Assemble pitas: Assemble pitas. Warm pita bread in a dry skillet or over a gas range until lightly toasted and pliable. Cut each pita in half and spread tzatziki on the inside of pita (I use ~2 Tbsp. tzatziki per pita half). Add a big scoop of cucumber-tomato salad and ~2 slices of halloumi per pita. Serve with extra tzatziki and lemon wedges, if desired.