Start by slicing your potatoes until they are roughly ½ a centimetre thick. Place these into a pan of boiling water, and par boil for 5-10mins or until they have just started to soften.
In the meantime, slice your onion and beef tomatoes thinly. Halve the cherry tomatoes and place to one side.
In a mixing bowl, combine together the passata, crème fraiche, garlic (crushed) and herbs. Make sure this is thoroughly mixed so that the passata and crème fraiche have formed a creamy sauce.
Once the potatoes have par boiled, take 1/3 of the potatoes and lay them across the base of an oven dish. Layer on top 1/3 of the tomatoes, onion and chicken. Pour over 1/3 of the sauce and repeat the process.
Once you have three layers of the potato/tomato/onion/sauce combination, top with a sprinkling of grated mozzarella.
Place into a pre-heated oven at gas mark 5 for 50mins or until the dish is bubbling and cheese golden.