Heat oil in a large skillet over medium heat. When hot, add onion, and garlic. Cook until just soft, about 4 minutes. Add chicken, salt, and pepper. Cook, breaking up meat with a spoon until meat is no longer pink, about 4 minutes. Stir in flour until evenly distributed. Stir in wine and cook until thickened, about 2 minutes. Remove from heat.
Stir in lemon juice, scallions, feta, and cream cheese. Let cool, and then stir in tarragon. Spoon mixture into a pastry bag or ziplock plastic bag. If using a plastic bag, cut off a corner. Pipe mixture into phyllo shells and sprinkle evenly with sesame seeds.
Preheat oven to 350ºF. Bake until heated through, about 8 minutes.
Tip: Make the filling up to three days ahead and store it in the refrigerator. The phyllo shells can be filled one hour before heating them.