Preheat oven to 375 degrees. Separate the crescent triangles as directed in the package. For each triangle, gently roll out the dough to expand sightly in size, while keeping the same triangular shape.
Fill each triangle with a few spinach leaves (don't worry about adding too much, they will shrink a ton once cooked) and some cheese, and roll out the croissants as directed in the package – taking care to not let the filling spill out.
Sprinkle the tops of the croissants with fresh cracked black pepper and bake for 15-20 minutes till lightly browned and done.