Cut out 12 x 13 cm (5 inch) squares of nonstick baking parchment and press a square into each section of a 12-section muffin tray. Mix together the flour, baking powder, salt and oregano in a bowl. Stir in the basil, spring onions and tomatoes.
Mix the buttermilk with the egg yolk, add to the bowl and stir until only just combined, sprinkling in a little more flour if the mixture is very sticky.
Turn out on to a lightly floured work surface and cut into 12 even-sized pieces. Shape each into a ball. Drop one ball into each of the lined tin sections.
Push your thumb into each ball to create a small cavity in the centre and insert a few pieces of goats' cheese into each. Brush with milk to glaze. Sprinkle with plenty of pepper.
Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for 15 minutes or until risen and beginning to colour. Transfer to a wire rack to cool.