Season the chicken breast cutlets evenly on both sides with the dried oregano, salt, and freshly ground black pepper.

Heat the olive oil in a large non-stick skillet or griddle pan over medium-high heat until hot and shimmering.

Add the seasoned chicken cutlets to the pan and cook for 3 to 4 minutes per side, until they are golden brown and cooked through.

Transfer the cooked chicken to a plate to rest, then place the halloumi slices directly into the same hot pan.

Sear the halloumi slices for 1 to 2 minutes on each side until they develop a beautiful golden crust and soften slightly.

While the cheese cooks, lightly toast the brioche burger buns until they are warm and golden brown.

Assemble the burgers by spreading tzatziki on the bottom buns, followed by baby spinach, a tomato slice, a chicken cutlet, and two slices of warm halloumi, then top with the remaining buns and serve immediately.