Cheesy Italian Chicken

• 500 g chicken breast
• 1 tbsp dried oregano
• 1 tbsp extra virgin olive oil
• 1 brown onion, sliced
• 2 garlic cloves, crushed
• 1 capsicum (red pepper), thinly sliced
• 800 g tin crushed tomatoes
• 1 cup Kalamatta olives, pitted
• 200 g bocconcini
• 100 g pesto
• 160 g rocket