Mix the flour and oatmeal in a bowl, then add the butter and rub in until the mixture resembles fine breadcrumbs. Add the water and mix to a firm dough. Turn out on to a lightly floured surface and knead briefly.
Roll out the pastry and line a 23 cm (9 inch) fluted flan tin, pressing evenly into the sides. Prick the base with a fork, chill for 15 minutes, then line with nonstick baking paper and add macaroni or baking beans. Bake blind in a preheated oven, 190°C (375°F), Gas Mark 5, for 10–15 minutes. Remove the paper and macaroni or beans and return to the oven for 5 minutes.
Mix the vegetables in a roasting tin. Add the garlic, oil and rosemary, coating the vegetables evenly. Season to taste. Roast at 200°C (400°F), Gas Mark 6, for 35 minutes or until the vegetables are tender.
Fill the pastry case with the cooked vegetables, scatter the feta cheese over the top and sprinkle with the Parmesan. Return the tart to the oven for 10 minutes.