Preheat grill on high. Place combined capsicum, skin-side up, under grill and cook for 8-10 minutes or until charred and blistered. Transfer to a sealed plastic bag. Set aside for 10 minutes (this helps lift the skin). Remove the skin from the capsicum and cut the flesh into thick strips.
Preheat oven to 200°C. Heat the oil in a large frying pan over medium-high heat. Add half the chicken and cook, turning occasionally, for 5 minutes or until browned. Transfer to a large baking dish. Repeat with the remaining chicken.
Add the onion to the pan and cook, stirring occasionally, for 5 minutes or until golden. Add the garlic and cook for 2 minutes or until aromatic. Add the wine and cook for 2 minutes or until reduced by half. Add the capsicum, passata, stock and thyme. Season with salt and pepper.
Pour the sauce over the chicken. Bake for 45 minutes or until chicken is cooked through. Stir in olives. Serve with mixed salad leaves.