Position a rack in the center of the oven and heat the oven to 450°F.
Prepare a medium (350°F to 375°F) gas or charcoal grill fire. Brush the onion slices with oil and season with salt and pepper.
Grill the onion slices until grill marks form on one side, about 7 to 8 minutes. Flip the slices and continue to grill until tender, about 7 to 8 minutes more. Stack the onions on a large piece of foil, wrap the onions up, and let them sit for 10 minutes to soften further. Coarsely chop the onions.
Generously coat a 9x13-inch rimmed baking sheet with oil. Oil your hands, then evenly press the pizza dough onto the sheet all the way to the corners. Using your knuckles, make dimpled depressions in the top of the dough.
In a small bowl, mix 2 Tbs. of the oil with 1 tsp. salt and 1 tsp. water; brush the dough with the mixture.
In a medium bowl, toss the sage and onion with 1 Tbs. of the oil. Top the dough with the onion mixture. Bake in the center of a 450°F oven until the flatbread is browned and the onions are slightly browned on the edges, 20 to 25 minutes. Season to taste with salt and pepper, slice, and serve.
nutrition information (per serving):
8, Fat Calories
70, Saturated Fat
5, Monounsaturated Fat
28, Polyunsaturated Fat
Photo: Scott Phillips