In the bowl of a stand mixer fitted with a dough hook, combine the flour, yeast, salt, sugar, oil, and water. Mix on medium speed for 10 minutes, until the dough is smooth and sticky.
With lightly oiled hands, shape the dough into a ball and place in a greased bowl. Cover with plastic wrap and let rise in the refrigerator for 10 hours. (For a quicker option, let rise at room temperature for 3 hours, though the flavor is better after a cold, overnight rise.)
The next day, wet your hands and gently stretch the dough into a round shape on a lined baking tray. In a small bowl, mix the olive oil, garlic powder, and dried parsley, then brush over the dough. Dimple the surface with your fingertips and sprinkle generously with coarse salt.
Preheat the oven to 430°F (220°C) on convection setting. Bake the focaccia for 13 to 15 minutes, until golden and puffed.
While the focaccia bakes, wash and dry the lettuce. In a small bowl, whisk together the olive oil, mayonnaise, Dijon, honey, lemon juice, garlic, Parmesan, salt, and cold water until creamy. Toss with the lettuce until well coated.
Let the focaccia cool slightly. Cut into wedges or serve whole, topped with the dressed salad.