Combine one cup very warm water (115-120°F) with sugar and yeast in a large bowl. Let stand until foamy, about five minutes. Add one tablespoon olive oil, the flour, and one and 1/2 teaspoon salt. Stir to form a sticky dough.

Turn out onto a floured surface and knead until smooth, about 10 minutes, dusting with flour.

Brush a large bowl with olive oil. Add the dough and loosely cover with plastic wrap. Set aside until doubled in size, about one hour and 30 minutes. Brush a rimmed baking sheet with olive oil. Stretch the dough on the baking sheet. Cover with a towel and set aside until doubled, about 30 minutes.

Preheat the oven to 475°F.

Scatter 3/4 of the cheese, bell pepper and scallion whites over the dough. Bake until the crust is golden, about 15 to 18 minutes.

Toss the arugula and scallion greens with the remaining tablespoon olive oil and salt. Sprinkle over the flatbread. Sprinkle the remaining cheese and bake for two to three more minutes or until cheese bubbles.