Heat a wood/charcoal fire until the embers are hot with a low flame. Place grill grates or grill pan over the hot embers and wait until the surface is very hot. Alternatively, you can preheat a gas grill to high or heat a grill pan on an indoor stovetop.

Dry cheese slices. Brush them with olive oil and season with black pepper. Place cheese on the hot grates or pan. Sear for about 3–4 minutes on one side only. Transfer to a warm plate using a metal spatula.

Lightly grill bread slices on one side. Slather one tablespoon of charred kale pesto on four slices of bread. Top each schmear with two pieces of grilled halloumi. Sprinkle with sea salt, lemon zest, and more pepper to taste. Top the sandwiches with the remaining four pieces of grilled bread and serve warm.