For green olives with tomatoes & preserved lemon, heat 2 tablespoons olive oil in the base of a tagine or heavy-based saucepan over a medium heat, stir in 1 finely chopped onion, 2 finely chopped garlic cloves and 2 teaspoons coriander seeds and cook for 3 minutes to let the flavours mingle. Toss in 16 large cracked green olives and add 1 x 400 g can chopped tomatoes and 1½ teaspoons sugar. Cover and cook gently for 15 minutes. Season to taste with salt and pepper, then stir in a small bunch of finely chopped coriander. Serve as an accompaniment to meat and poultry tagines.