Preheat the oven to 180°C fan. Line a 12-hole muffin tin with paper muffin cases.
In a large bowl, whisk together the eggs, olive oil and yoghurt until well combined.
In a separate bowl, combine the wholemeal flour, self-raising flour, bicarbonate of soda, baking powder, salt and black pepper.
Gradually add the dry ingredients to the egg mixture, stirring gently with a whisk or spatula until you have a smooth, fairly thick batter. Do not overmix, as this will help keep the muffins light and fluffy.
Add the cubed halloumi, grated cheddar, grated Edam, crumbled feta and chopped fresh mint. Gently fold everything together with a spatula until the cheeses and mint are evenly distributed throughout the batter.
Divide the mixture evenly between the 12 muffin cases using an ice-cream scoop or two spoons. Fill the cases almost to the top, as the muffins will rise during baking.
Transfer to the preheated oven and bake at 180°C fan for 20–25 minutes, or until the muffins are well risen and golden brown on top and a skewer inserted into the centre comes out almost clean.
Leave the muffins to cool in the tin for 5 minutes, then transfer them to a wire rack. Serve warm or at room temperature.