Preheat the oven to 190 degrees C. Loosen the skin on each chicken breast and tuck a sprig of rosemary underneath, between the skin and the flesh. Place the chicken in a large roasting tin and roast for 5 minutes.
Combine the eggplant, zucchini and red capsicum in a bowl. Drizzle the oil over the vegetables, then toss to coat. Push the chicken portions to one side in the roasting tin, then add the vegetables. Roast the vegetables and chicken for 20 minutes, then turn the vegetables. Roast for a further 5–10 minutes until the vegetables are well browned and tender and the chicken is cooked through.
Meanwhile, make the crumble topping. Put the oats in a food processor and pulse briefly to make a fairly fine ‘flour’. Add the butter, then pulse again until the mixture comes together in small lumps. Pat the sun-dried tomatoes on paper towel to blot up excess oil, then snip into small pieces with kitchen scissors. Stir into the crumble mixture with the oregano.
Transfer the roasted vegetables to a baking dish, and stir in the tomatoes with their juice, and the black olives. Season to taste. Cover and cook in the oven for 10 minutes. Meanwhile, discard the chicken skin and rosemary sprigs, then remove the chicken meat from the bone and cut into large bite-sized pieces.
Stir the chicken into the vegetable mixture, then scatter the crumble topping over the top, making sure to cover any vegetables that are already browned. Bake, uncovered, for 20 minutes until the topping is crisp and golden, then serve.