Delicious and hearty lamb shank casserole

Ingredients

• 2 tablespoons plain flour
• 6 (1.8kg) trimmed lamb shanks
• 2 tablespoons olive oil
• 1 brown onion, roughly chopped
• 1 garlic clove, crushed
• 2 medium carrots, peeled, roughly chopped
• 200g button mushrooms, thickly sliced
• 2 celery stalks, roughly chopped
• 1/4 cup tomato paste
• 1/2 cup red wine
• 400g can crushed tomatoes
• 2 cups beef stock
• 1 large zucchini, roughly chopped
• Mashed potato, to serve
• Salt, to season