Preheat oven to 350°. Coat a 9x5-in. loaf pan with cooking spray., In a large bowl, beat butter and sugar until crumbly. Add eggs, 1 at a time, beating well after each addition. Beat in oil, lemon juice, zest, vanilla and, if desired, poppy seeds. In another bowl, whisk flour, baking powder and salt; add to creamed mixture alternately with yogurt, beating after each addition just until combined., Transfer to prepared pan. Bake 50-60 minutes or until a toothpick inserted in center comes out clean. Cool in pan 10 minutes before removing to a wire rack to cool completely. If desired, top with candied lemon slices.