Squeeze water out of thawed spinach using a few paper towels. Pinch perforated edges of crescent roll dough together. Using a rolling pin, roll out crescent dough on a parchment (or silicone mat) lined baking sheet until shaped into a nice rectangle.
In a small bowl, mix together feta, spinach, onion powder, and salt. Pour and spread mixture onto crescent dough.
Roll up crescent dough and cut into 9 even pieces. Lay cross section face up. Reshape into pretty circles and flatten with the palm of your hand. Crack the egg into a bowl and whisk lighting with a fork. Using a pastry brush, coat the top of each pinwheel with egg wash.
Bake in the oven for approximately 20 minutes until golden brown.