For poolish: In a medium bowl, stir together flour, water, and yeast until flour is completely moistened. Cover with plastic wrap, and let stand at room temperature for 8 to 12 hours.
For dough: In the bowl of a stand mixer fitted with the paddle attachment, place poolish. Add water and oil. Add flour, salt, and yeast, and beat at low speed for 4 minutes. Scrape down sides of bowl. Increase mixer speed to medium, and beat until dough pulls away from sides of bowl and forms a ball on paddle, 2 to 3 minutes. (To test if dough is ready, perform a windowpane test; see Notes.)
Oil a large bowl. Place dough in prepared bowl. Cover with plastic wrap, and let rise in a warm, draft-free place (75°F/24°C) for 1½ hours, folding dough in bowl every 30 minutes. (To fold, use floured hands to reach under one side of dough; gently stretch up, and fold over center. Repeat 3 more times around bowl. See Notes.) Watch video below for folding tips.
Line a rimmed baking sheet with parchment paper; dust with flour.
On a heavily floured surface, turn out dough (use bowl scraper to help to keep dough from tearing and losing air pockets). Flour hands; using your fingertips, gently stretch dough into a 15x8½-inch rectangle, re-flouring hands as needed. Lift dough with two hands, and place on prepared pan. Using your fingertips, dimple surface of dough. Dust top generously with flour. Cover and let rise in a warm, draft-free place (75°F/24°C) until almost doubled in size, about 1 hour.
Preheat oven to 425°F (220°C).
Bake until golden and an instant-read thermometer inserted in center registers 205°F (96°C), 12 to 15 minutes. Let cool on pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.