Slice the chicken breasts thinly across and place them in a bowl with the lemon juice, paprika and garlic.
Chop the tarragon and add to the bowl. Stir to coat the breasts evenly and leave to absorb the flavours for at least 30 minutes - I do this in the morning and leave in the fridge until I need them in the evening.
Melt the butter in a large, deep, heavy based frying pan over a fairly low heat. Add the chicken mixture and cook gently, stirring now and then for 8-10 minutes until the chicken is cooked through.
Remove chicken slices to a plate and put to one side. Slice the tomatoes into 3-4 pieces - if you can get the ones in jars of oil they are nice and soft.
Bubble the pan juices up fiercely for two minutes to reduce them slightly, remove pan from heat and add the cream. Bring back to boil and boil, stirring for 2-3 minutes or until it has thickened slightly.
Season to taste with salt and chilli and then return cooked chicken and tomatoes to the sauce, stir for another minute or so.
Spoon into a shallow serving dish and cover loosely with foil. This may now be kept warm for up to an hour without spoiling in a low oven. Just before serving scatter with rocket leaves.