Position the oven rack in the middle and preheat to 350°F / 180°C (160°C fan).
Line an 8x8-inch (20x20 cm) baking dish with parchment paper, ensuring the paper overhangs the sides for easy removal.
In a large mixing bowl, whisk the yogurt, brown or white sugar, and vanilla extract until smooth.
Sift in the flour, baking powder, and salt. Stir until the mixture is combined.
Add the rolled oats, chopped dried fruit, and seeds/nuts (or your choice of substitutes). Mix until well combined.
Transfer the mixture into the prepared baking dish, spreading it evenly with a spatula.
Bake for 20-25 minutes, or until golden brown and a toothpick inserted into the center comes out clean.
Remove from the oven and let it cool in the pan for 10 minutes. Then transfer to a cooling rack and cool for about 20 minutes before slicing into squares or rectangles.