Cut the chicken fillets in half horizontally to form two flatter fillets from each piece. Season with dried oregano, salt and pepper.
Heat 1 tbsp olive oil in a dutch oven (or medium to large pot with a lid). Once hot, fry each fillet half on both sides until golden brown. Remove from the pot and set aside.
Add 1 tbsp olive oil along with the diced shallot to the dutch oven. Sauté until translucent. Add the garlic and briefly sauté until fragrant.
Add the tomatoes and balsamic vinegar and cook on medium heat for 5-10 minutes until starting to caramalise.
Add the orzo and stir to coat in the pan juices. Toast the orzo lightly for a few minutes.
Pour over the chicken stock and stir. Cover and cook on a low heat (at a gently simmer) for 10-15 minutes, until most of the water has cooked off and the orzo is almost done.
Place the chicken fillet pieces on top of the orzo and top each one with a slice of mozzarella. Cover and cook for a further 3-5 minutes, or until mozzarella has melted.
Top the chicken orzo with several dollops of fresh basil pesto and fresh basil leaves. Drizzle with olive oil and serve.