Coat the inside of a 6-quart slow cooker with the softened butter and add the brioche cubes.
Whisk the pumpkin, eggs, milk, brown sugar, vanilla, cinnamon, ginger, nutmeg and salt until smooth.
Pour the custard over the bread, fold gently until every cube is damp and scatter the pecans over the top.
Let the mixture stand in the cooker for 15 minutes so the driest bread absorbs custard.
Cover and cook on low until the center reaches 165°F and no liquid custard appears when pressed, 2 1/2 to 3 hours.
Turn off the cooker, uncover and rest the pudding for 15 minutes before scooping.