Cook spinach according to package directions. Add salt to taste. Strain out all water.
Remove sausage from casing; break or cut into small pieces. Fry in 1/4 c. oil. Stir to cook evenly. Remove sausage from pan and set aside. Add 1/4 c. oil to pan. Fry sliced onions (or diced) until golden brown. Remove onions from pan. Season with salt.In same pan stir in spinach until all oil is absorbed. Cool onion, spinach and sausage.
Dissolve yeast in 1/2 c. warm water. Combine flour, sugar and salt in large bowl. Make well in flour mixture and add oil and yeast; stir to blend. Add remaining water. Work to form dough. Place dough on floured board and knead 10 minutes until smooth. Place in oiled clean bowl and cover. Let rise until double.
Roll half dough into a rectangle to fit pan like pie dough. Make a layer of each ingredient.. sausage, spinach, onion. Roll out other half of dough to fit over top. Crimp edges like pie crust. Make slits for steam to escape. Brush with beaten egg. Cover. Let rise 1/2 hour.
Bake 35-40 minutes at 350 degrees in lightly coated 13 x 9 inch pan with oil. May be removed from pan after 15 minutes and placed on platter.
I always prepare and cook mine in the same dish I plan to serve it in. Serve hot or warm.