Step 1Combine yoghurt, honey (if using) and vanilla extract in a bowl. Line a sieve with muslin, or a clean chux, and set over a clean bowl. Spoon yoghurt mixture into the muslin, then draw up the edges to make a tight parcel and secure with kitchen string. Refrigerate overnight until firm; discard liquid in the bowl.
Step 2Process flour, table spread and caster sugar in a food processor until the mixture resembles fine breadcrumbs. Add chia seeds and 2 tablespoons chilled water; process until dough just comes together, adding more chilled water, if necessary. Turn pastry onto a lightly floured surface. Knead until smooth. Shape pastry into a disc. Cover with cling wrap and refrigerate for 30 minutes.
Step 3Preheat oven to 160°C. Spray a 2cm-deep x 12.5cm x 35cm loose-based rectangular tart tin with oil. Roll out pastry between 2 sheets of baking paper until 5mm thick. Line tin with pastry. Trim off the excess with a sharp knife. Refrigerate for 10 minutes.
Step 4Place tart tin on a baking tray. Line pastry case with baking paper. Fill with ceramic pie weights or uncooked rice and bake for 15 minutes, or until edges are light golden. Remove weights and paper. Bake for a further 10 minutes, or until the base is golden. Set the pastry case aside to cool completely.
Step 5Spread yoghurt mixture over base of the pastry case. Arrange the fruit slices on top and serve.