Grease a 23 x 33 cm / 9 x 13-inch baking dish with butter or cooking spray.
Cut the Hawaiian rolls into quarters or tear them into roughly 1-inch pieces. Spread the pieces evenly in the prepared baking dish.
In a large bowl, whisk together the eggs, whole milk, heavy cream, pumpkin purée, brown sugar, vanilla extract, pumpkin pie spice, cinnamon, and salt until smooth.
Pour the pumpkin custard evenly over the Hawaiian rolls. Gently press the bread pieces into the custard so they are moistened.
Cover the dish and refrigerate for at least 4 hours or overnight. For a same-day version, let it stand for 15 minutes while preparing the topping.
When ready to bake, preheat the oven to 175°C / 350°F.
Make the streusel topping. In a small bowl, combine the flour, brown sugar, cinnamon, and chopped pecans. Add the cold butter and work it into the mixture with a fork or your fingertips until crumbly.
Sprinkle the streusel evenly over the soaked Hawaiian rolls.
Bake uncovered for 35 to 40 minutes, until the top is golden and the center is set. Loosely cover with foil during the final 10 minutes if the top browns too quickly.
Let the casserole rest for 10 minutes before slicing. Serve warm with maple syrup, whipped cream, pecans, powdered sugar, or your favorite toppings.