Preheat the oven to 150C/300F/Gas 2
For the garlic tomatoes, lay the tomatoes on a baking sheet with the cut side facing up. Place a piece of sliced garlic and some thyme leaves on each one. Season with salt and freshly ground black pepper.
For the skordalia sauce, cut the garlic heads in half horizontally across the centre and place in a roasting dish.
Place the cut garlic heads and the prepared garlic tomoatoes in the oven and cook them at 150C/300F/Gas 2 for about 45 minutes to 1 hour. Scoop out the insides of the soft garlic.
Place the potatoes in a pan of cold salted water and bring to the boil until soft and then drain. Pass through a potato ricer and set aside.
Meanwhile for the fish, turn the oven up to 200C/400F/Gas 6.
Put each fillet on a piece of aluminium foil, dot with butter, squeeze over the lemon and season. Add a few sprigs of parsley. Wrap up the foil parcels loosely so they are sealed but have room around them. Place in the oven for 8-10 minutes.
To finish the sauce, combine the mashed potato with the roasted garlic in a bowl. Add the almonds and lemon juice. Season well and then add the oil gradually.
Take the fish from the oven and serve each fillet with some of the sauce, the tomatoes, watercress and toasted flaked almond.
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