Preheat oven to 375 degrees F.
Drain spinach and remove excess moisture. Place ricotta in a cheesecloth-lined colander, and let drain 2 hours. Combine ricotta, 2 tablespoons Parmesan and cornstarch; stir well. Add drained spinach, green onions, basil, oregano, thyme, and salt; stir well.
Beat egg whites at high speed until stiff peaks form. Fold one-fourth of beaten egg white into spinach mixture; gently fold in remaining egg white.
Place 1 sheet of phyllo on a damp towel (keep remaining phyllo covered); lightly coat phyllo with cooking spray. Repeat layers twice. Spoon half of spinach mixture along short side of phyllo, leaving 1-inch borders on outer edges and a 2-inch border at short end. Fold short edge of phyllo over filling.
Fold lengthwise edges in 1-inch, and roll up, jelly roll fashion. Lightly coat phyllo roll with cooking spray. Place, seam side down, on a baking sheet coated with cooking spray; pierce top several times with tip of sharp knife, and sprinkle with 1 tbsp of Parmesan. Repeat procedure with remaining phyllo, spinach mixture and Parmesan.
Bake at 375 for 35 to 40 minutes or until crisp and golden. Cut each strudel in slices and serve hot or room temperature.