Preheat oven to 325°F In a saute' pan sprayed with non-stick cooking spray. Saute the onions until golden in color. Add scallions and sauté 2-3 minutes. Add the parsley, dill, salt & pepper. Stir in spinach. Blend thoroughly. Remove from heat and cool before proceeding further.
Place cooled spinach mixture in electric mixing bowl using the paddle (or large bowl if mixer is unavailable). On low speed, add eggs, one at a time. Add feta, and cream cheese (in chunks).Mix well, but do not over mix.
Carefully unroll phyllo sheets. Place 9x13x2 casserole dish over phyllo and using sharp knife, cut phyllo to fit pan. Grease bottom and sides of casserole pan with non-stick cooking spray.
Place 8-10 sheets of phyllo, one sheet at a time on bottom of pan, spraying each sheet individually with cooking spray (while layering). Add spinach mixture, spreading out evenly over phyllo sheets. Top with remaining phyllo sheets, again, spraying each sheet with cooking spray as was done for the bottom of pan.
Brush on the melted butter over top of casserole. With a sharp pointed knife, score the top layers of phyllo into serving portions. (triangle shape is traditional). Bake at 325°F for 45 minutes. Watch phyllo for burning. Color should be a light golden brown. Remove from oven and let stand about 15 minutes before serving.