Heat your oven to 200°C/Fan 180°C/Gas 6. Roughly chop the tomatoes and put in a roasting tin. Trim the dry ends off the fennel and thickly slice it. Add to the tin. Drizzle over 1 tbsp oil. Season. Drop in the unpeeled garlic clove. Roast for 30 mins till the veg are soft and charred.
Meanwhile, peel and chop the onion. Peel and grate the ginger. Set the coriander leaves aside. Finely chop the stalks.
Heat ½ tbsp oil in a pan over a low heat. Add the onion and season. Fry for 5-6 mins till golden and soft. Stir now and then. Add the ginger and coriander stalks. Stir. Pour in the coconut milk and 500ml boiling water.
Pluck the garlic clove from the tray. Squeeze out the flesh into the pan. Tip in the roast veg. Simmer for 5 mins.
Ladle the soup into a blender and blitz till smooth, or use a hand-held blender. Squeeze in a little lemon juice. Taste and add more seasoning or lemon juice if it needs it. Stir in most of the coriander leaves. Ladle into bowls. Garnish with the rest of the coriander.