Heat oven to 350°. Grease 2 (9" x 5" x 2¾") loaf pans with butter and dust with flour; set aside. Whisk flour, baking powder, cinnamon, and salt in a large bowl; set aside.

In a separate bowl, whisk sugar, oil, and eggs.

Pour wet ingredients over dry ingredients and whisk until just combined.

Stir in strawberries and pour batter into prepared pans. If using jam, spoon ¼ cup over each loaf and using a knife, swirl jam into batter.

Bake until golden brown and a toothpick inserted in the middle of the loaves comes out clean, about 1 hour.

Let cool for 30 minutes before slicing and serving.