Place the water and butter into a medium frying pan with a lid over a high heat and bring to the boil.
Add the carrots, celery, leeks, courgettes and tarragon and bring back to the boil.
Season the chicken breasts with salt and freshly ground black pepper and place into the pan on top of the vegetables. Cover with a lid and simmer for 6-7 minutes, or until the chicken is almost completely cooked through.
Add all of the wild mushrooms except the trompettes and replace the lid and cook for one minute.
Add the trompettes and continue to cook for 30 seconds.
Place the garlic, shallots and parsley into a bowl and mix well (this mixture is called a persillade.
Add the persillade and tomatoes to the pan and season, to taste, with salt and freshly ground black pepper.
Test the chicken is cooked by inserting a skewer into the thickest part of the breast - if the juices run clear the chicken is cooked. If the juices are not clear, replace the lid and cook for 1-2 minutes more, or until completely cooked through.
To serve, remove the chicken breasts from the pan and cut in half on the diagonal. Spoon some of the vegetables onto each plate and top each pile with two pieces of chicken. Add a further spoonful of vegetables and drizzle with the cooking juices.