Preheat oven to 180°C.
Spray pan with non-stick baking spray. (I used PAM)
Whisk flour, baking powder, and salt in mixing bowl.
Add sugar and lemon zest into mixing bowl.
Use fingers to rub together most of the sugar with lemon zest, until sugar is moist.
Add yogurt, oil, eggs, and vanilla extract in measuring cup.
Whisk to blend.
Then fold in wet ingredients to dry ingredients, until just combined.
Pour batter into prepared pan and smooth top.
Drop dollops of jam on top of batter.
Use a skewer or back of knife to create swirls.
Bake until top of cake is golden brown or until a skewer inserted into center comes out clean, about 50–55 minutes.
Let cake cool in pan on a wire rack for 15 minutes.
Then de-mould and allow to cool completely on wire rack.