Whisk together oil and sugar in a large mixing bowl. Add lemon zest, lemon juice, eggs and sour cream; whisk till very well mixed.
Whisk together flour, baking powder, and salt in a small bowl. Stir into wet ingredients. Toss berries with the 1 teaspoon of flour and gently fold into the batter. (If using frozen berries, toss them with 2 teaspoons of flour.)
Divide batter between the three pans. Bake at 325° for about 40 minutes or until toothpick comes out clean. Cool in pan for 5 minutes, then remove to cooling racks.
If desired whisk together the powdered sugar and lemon juice and drizzle over loaves.