1. Preheat oven to 450°.
2. Combine the first 3 ingredients in a medium bowl, and let stand for 5 minutes or until bubbly. Weigh or lightly spoon 5.6 ounces flour (about 1 1/4 cups) into dry measuring cups, and level with a knife. Stir 4 teaspoons olive oil into yeast mixture. Add flour, 1/4 teaspoon salt, and 1/4 teaspoon black pepper to yeast mixture, stirring until a soft dough forms. Knead dough on a lightly floured surface until smooth and elastic (dough will be soft and tacky).
3. 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, 45 minutes or until doubled in size. Punch dough down; cover and let rest 5 minutes.
4. Drizzle 2 teaspoons oil into an 11 x 7inch glass or ceramic baking dish. Press dough into dish. Cover loosely with plastic wrap, and let rise in a warm place (85°), free from drafts, 30 minutes or until puffy; sprinkle dough with 1/4 teaspoon salt, nuts, onion, and thyme. Bake at 450° for 18 minutes or until golden.
5. Place arugula in a bowl; drizzle with remaining 1 tablespoon oil and juice. Toss. Turn bread out onto a work surface; top evenly with prosciutto. Slice bread into 4 (2 3/4 x 7inch) rectangles. Top each serving with about 1/2 cup arugula mixture; sprinkle evenly with remaining 1/8 teaspoon salt. Top with cheese.