Stir together first 6 ingredients. Cover and chill until firm.
Sprinkle fish fillets evenly with 1/4 teaspoon salt and 1/4 teaspoon pepper. Divide butter mixture into 4 portions; shape each portion into a ball. Place 1 ball of butter mixture at end of each fillet; carefully roll up fillets, keeping butter mixture inside.
Unfold phyllo; cover with plastic wrap and a damp towel to prevent drying. Place 1 sheet of phyllo on a flat surface. Spray half of phyllo sheet with cooking spray. Fold sheet in half crosswise; spray again. Repeat procedure with a second sheet of phyllo; stack the sheets.
Place 1 fillet in the middle of stacked phyllo sheets. Gather corners of sheets together to form a bundle. Twist slightly; tie bundle with kitchen twine. Spray bundle with cooking spray. Place bundle on rack of a lightly greased broiler pan. Repeat procedure with remaining phyllo sheets and fillets.
Bake at 450° for 15 minutes or until golden. Serve immediately with gourmet salad greens, if desired.