Sauté onion in 1 teaspoon oil in skillet for 3 minutes.
Combine spinach, Feta and mint in bowl. Stir in egg white and onion.
Carefully unroll phyllo dough on cutting board. Cut stack lengthwise into thirds. Stack thirds into one pile. Cover dough with plastic wrap.
Remove one strip of dough from pile and lay flat on work surface. Lightly coat with cooking spray. Very lightly sprinkle with crumbs. Repeat with 2 more layers, stacking on first for total of 3 layers. Place scant tablespoon spinach mixture on one end of stack. Fold dough over to form triangle; continue folding triangle to end of strip. Place triangle packet on ungreased baking sheet. Repeat with remaining dough and filling.
Meanwhile, heat oven to 375 degrees F.
Bake in 375 degree F oven 15 minutes until golden. Serve warm or at room temperature. Makes 2-1/2 dozen triangles.