Preheat oven to 350°F (180°C). Spray an 8½x4½-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan.

In the bowl of a stand mixer fitted with the paddle attachment, beat granulated sugar, oil, and lemon zest at medium speed until fluffy, 2 to 3 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition.

In a medium bowl, whisk together flour, baking powder, and salt. In a liquid-measuring cup, combine buttermilk and 3 tablespoons (45 grams) lemon juice. With mixer on low speed, gradually add flour mixture to sugar mixture alternately with buttermilk mixture, beginning and ending with flour mixture, beating just until combined after each addition. Using an offset spatula, spread batter into prepared pan. Wipe offset spatula clean, and dip into oil. Using oiled offset spatula, score a 3- to 4-inch line lengthwise down center of batter.

Bake until a wooden pick inserted in center comes out with a few moist crumbs, 45 to 50 minutes. Let cool in pan for 15 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack.

In another small bowl, whisk together confectioners’ sugar, melted butter, and remaining 2 tablespoons plus 2 teaspoons (40 grams) lemon juice until smooth; pour onto cooled cake. Let stand until glaze is set before serving, about 10 minutes. Store in an airtight container for up to 3 days.