Short ribs:

In large sealable freezer bag, combine pineapple juice, ¾ cup water, sugar, gingerroot, garlic and lemon zest. Add short ribs and refrigerate for 6 hours or overnight. Remove beef from marinade; set marinade aside. Pat beef dry with paper towels. Season all over with salt and pepper. Heat half of oil in Dutch oven over medium-high heat. Brown beef in batches, adding more oil as needed, until browned all over, about 10 minutes. Transfer beef to plate; set aside.

Add reserved marinade and stock to Dutch oven. Cook over medium heat, stirring up any browned bits from bottom of pan. Return beef and any accumulated juices to pan; bring to boil. Transfer to 325˚F oven and cook for 2 hours, until fork tender.
Remove beef from sauce and let cool. Meanwhile, combine cornstarch with 2 tbsp water until smooth; whisk into beef cooking sauce, and cook, stirring, over medium heat until sauce thickens, about 2 minutes. Remove bone and any fat from the beef; shred beef by pulling with 2 forks. Return beef to sauce and reserve for sandwich.

Roasted Garlic Mayonnaise:

Slice top ¼ inch off heads of garlic to expose cloves. Place each head upright on sheet of foil; drizzle with oil and bundle up with foil. Place in small oven-proof pan and roast in oven alongside the beef until heads are soft, about 1 hour. Remove from oven and let garlic cool.

Unwrap roasted garlic heads; squeeze garlic cloves from skins into small bowl. Mash with fork and stir in mayonnaise, lemon juice and sriracha sauce.

Pickled Veggies:

Place carrots or broccoli slaw in bowl. In saucepan bring vinegar, 1 cup water, sugar, garlic, red pepper flakes and salt to boil. Pour hot brine over carrots. Stir in cilantro. Let cool completely.

To Assemble:

Spread baguette pieces with mayonnaise and top with warm shredded beef, pickled veggies, cilantro leaves and cucumber. Top with baguette tops and serve.

Make Ahead Tip

Pickled vegetables can be made ahead, cover and refrigerate overnight or up to 1 week.