In a large flat casserole, heat oil. Add onions and sweat until translucent. Add flour and combine well with oil and onion. Add the rest of the vegetables and sweat together. Season mixture with salt and pepper. Add garlic and cumin. Add broth and boil for 3 minutes. Transfer mixture to a baking casserole.
Prepare pastry dough:
In a bowl combine flour, baking powder and salt with a fork. Work in butter with hands until mixture resembles coarse meal. Stir in milk. Sprinkle workspace with flour. Lay out dough and work to size of baking dish.
Place dough over casserole. Bake 45 minutes, until browned. Serve immediately.