Preheat the oven to 350°F (175°C). Line a 9 by 5 inch loaf pan with a parchment sling and lightly grease the sides.

In one bowl, whisk together the flour, baking powder, baking soda, and salt until combined.

In another bowl, whisk together the sugar, oil or melted butter, eggs, yogurt, and vanilla until smooth. Add lemon zest if using.

Fold the dry ingredients into the wet ingredients with a spatula until just blended, making sure not to overmix.

Spread half of the batter into the prepared pan and dollop half of the strawberry jam over it. Repeat with the remaining batter and jam.

Using a butter knife, gently swirl through the batter in an S pattern to create ribbons.

Bake in the preheated oven for 48 to 58 minutes, starting to check at 45 minutes. The loaf is done when a toothpick comes out with a few moist crumbs.

Allow the loaf to cool in the pan for 15 minutes before lifting it onto a rack with the parchment. Cool completely before slicing.

Optional: Mix powdered sugar with milk and a splash of vanilla or lemon; drizzle over the cooled loaf.