Preheat the oven to gas 5, 190°C or fan 170°C and cook the garlic and herb chicken as instructed on the pack, ensuring no pink is showing. Meanwhile put the sliced mushrooms in a microwavable bowl with a splash of water, cover with cling film and microwave for 2-3 minutes or until softened and cooked through. Drain and pat dry. Put the soft cheese in a small pan with the garlic and 100ml water. Heat over a low heat, stirring well until the cream cheese and water are melted together. Bring just to the boil, then stir in the mushrooms, peppercorns and the tarragon. Season a little with salt to taste. Meanwhile bring a pan of water to the boil and cook the beans for 3 minutes, drain and dress with the lemon juice. Serve the chicken with the mushroom sauce and green beans.