To prepare crust, dissolve yeast and sugar in warm water in a large bowl, and let stand 5 minutes. Lightly spoon flour into dry measuring cups, and level with a knife. Add 1 1/4 cups flour and 1/4 teaspoon salt to yeast mixture; stir until a soft dough forms. Turn dough out onto a floured surface. Knead until smooth and elastic (about 10 minutes); add enough of the remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
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, for 30 minutes or until doubled in size. (Press two fingers into dough. If indentation remains, the dough has risen enough.)
Punch the dough down; cover and let rest 5 minutes. Roll dough into a 12-inch circle on a floured surface. Place dough on a 12-inch pizza pan or baking sheet sprinkled with cornmeal. Crimp edges of dough with fingers to form a rim. Cover and let rise 10 minutes or until puffy.
Preheat oven to 450°.
To prepare pesto, place cilantro and next 5 ingredients (cilantro through 1/2 teaspoon salt) in a food processor, and process until smooth, scraping sides of bowl occasionally.
To prepare the pizza, heat a large nonstick skillet coated with cooking spray over medium-high heat. Add the mushrooms; cook 5 minutes or until moisture evaporates, stirring constantly. Add the vinegar, and cook until liquid evaporates. Sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Spoon the mushroom mixture onto pizza crust. Drop pesto by teaspoonfuls onto pizza crust. Top with onion, and sprinkle with fontina. Bake at 450° for 15 minutes or until the crust is lightly browned. Let stand for 5 minutes.