Preheat the oven to 250°F.
Separate the Hawaiian rolls, slice into thirds vertically, and arrange them on a baking sheet. Place in the oven for 3–5 minutes to lightly dry them out. This helps the rolls soak up the pumpkin mixture without becoming too soggy.
In a wide, shallow bowl, whisk together the eggs, milk, pumpkin puree, vanilla extract, cinnamon, and pumpkin pie spice until smooth and well combined.
Heat a large skillet or griddle over medium heat and add enough butter to lightly coat the surface.
Working in batches, quickly dip each Hawaiian roll into the pumpkin mixture, coating all sides. Don't let the rolls soak for too long. Allow any excess mixture to drip back into the bowl.
Place the coated rolls onto the hot skillet and cook for about 2–3 minutes per side, turning as needed, until golden brown on all sides and cooked through.
Repeat with the remaining Hawaiian rolls, adding more butter to the skillet between batches as needed.
Transfer the pumpkin French toast to a serving platter and dust with powdered sugar.
Serve warm with plenty of maple syrup.