Dissolve yeast and sugar in warm water in a large bowl; let stand 5 minutes. Add salt; stir to dissolve.
Lightly spoon flour into dry measuring cups; level with a knife. Add 2 1/2 cups flour to yeast mixture, stirring until a soft dough forms. Turn dough out onto a floured surface. Knead until smooth and elastic (about 8 minutes). Add enough of remaining 1/4 cup flour, 1 tablespoon at a time, to prevent dough from sticking to hands.
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, about 45 minutes or until doubled in size. (Gently press two fingers into dough. If indention remains, dough has risen enough.)
While dough rises, heat oil in a large nonstick skillet over medium-low heat. Add onion; cover and cook 30 minutes or until onion is tender, stirring occasionally. Uncover and cook 5 to 10 minutes or until onion is golden brown and most of liquid evaporates, stirring often.
Punch dough down. Pat dough into a jelly-roll pan coated with cooking spray. (If dough resists stretching, let rest 5 minutes before proceeding.) Spread onion evenly over dough. Sprinkle walnuts and Gorgonzola evenly over top; cover and let rise in a warm place 30 minutes or until doubled in size.
Preheat oven to 400°
Bake at 400° for 25 to 30 minutes or until lightly browned. Cut into 15 pieces.