Clean mushrooms. Leave caps whole, but chop stems coarsely. Fry in half a cup of oil till soft. Set aside to drain.
Peel onions, quarter lettuce & slice tomatoes. Add to a frying pan with celery, lemon juice, tomato paste, thyme, bay leaf, coriander, wine & the rest of the oil. Season & simmer for 20 to 25 minutes. Onions should be tender.
Remove mushrooms to a shallow dish & bring remaining ingredients to a rapid boil for 4 minutes. Pour over mushrooms & chill till ready to serve.