PREHEAT the oven to 350°F and line an 18-by-13-inch baking sheet with parchment paper.
UNROLL the crescent dough (do not separate into individual pieces) and pat into an 8-by-12-inch rectangle, gently pressing the seams closed.
BRUSH evenly with the mustard and then then top with the spinach, cheddar, scallions and peppers, leaving a ½-inch border all the way around. Sprinkle with ½ teaspoon salt.
ROLL the dough sheet into a log, starting with a short side.
SLICE into 8 pinwheels and transfer to the prepared baking sheet.