Combine mozzarella and feta cheese and spinach in a bowl. Stir to combine.
Lay out crescent roll triangles and add about 2 tablespoons of the cheese spinach mix to each roll. Then roll up each crescent with fold side facing down.
Add rolls to a non-stick pan or use a silicone mat (works very well!). Brush egg white on top of each roll if desired.
Bake for 12-14 minutes or until crescent rolls are golden brown.