Bring a large pan of salted water to the boil and cook the orzo following pack instructions. Meanwhile, mix the chopped oregano in a small bowl with the oil and brush some over the halloumi. Heat a large, non-stick frying pan and cook the halloumi for a few mins each side until golden and soft.
Drain the cooked orzo and mix with the tomatoes, olives and pesto. Season to taste. Spoon onto a serving plate and top with the halloumi. Drizzle over any remaining oregano oil and scatter over the leaves.