Slice the brisket against the grain along the length of it every 4 inches. Put the chunks into a deep rectangular pan along with the spices.
Roast, covered, 4 hours at 250 degrees or until tender and much of the fat renders. Shred the meet loosely with tongs then return to the oven, uncovered, another 1 hour. Drain off most of the fat and taste for salt. Keep warm until ready to serve.
Dice the mango and set aside. Halve the red onions from pole to pole then cut into thin strips vertically. Put them in a pot and cover with the vinegar and three cups water and a generous pinch of salt. Bring to a boil on the stove then set aside to cool. Strain the liquid out and dice the onions, then toss them with the mango. Refrigerate 'til ready to use.
To assemble the sandwiches, slice the baguette lengthwise along one side, leaving a hinge on the other. Lay slices of mozzarella along the bottom of the baguette. Lay 5 oz. of the warm shredded beef on top of that. Spoon the mango/pickle relish to taste over the meat. Gently close the baguette top and bottom together and wrap in parchment, wrapping one end and leaving the other unwrapped. Enjoy!!
Source: Addy Bittner, Portland