Heat a large skillet over medium-high heat. Add the Italian sausage and cook, breaking it up with a wooden spoon, until browned and cooked through, about 8-10 minutes. Drain off excess fat and let cool for 5 minutes.

In a medium bowl, combine the cooked sausage, softened cream cheese, shredded cheddar, garlic powder, and red pepper flakes if using. Mix until well blended. The mixture should be thick and spreadable.

Preheat oven to 375 degrees F. Line a baking sheet with parchment paper. Unroll both cans of crescent dough and press the perforations together to form two solid rectangles, each about 9x13 inches.

Divide the sausage mixture evenly between the two dough rectangles, spreading it to within 0.5 inch of the edges. Starting from the long side, roll each rectangle into a tight log. Place seam-side down and refrigerate for 10 minutes to firm up - this makes slicing much cleaner.

Using a sharp knife, cut each log into 8 equal slices, about 1 inch thick. Arrange pinwheels cut-side up on the prepared baking sheet, spacing 1 inch apart. Bake until golden brown and the dough is cooked through, 18-22 minutes.

Transfer to a serving platter, garnish with chopped parsley, and serve warm with marinara sauce for dipping.