Preheat a grill to high.
In a deep small bowl or storage container, combine the vinegar, 1/4 cup of water, sweetener, salt, 1/8 teaspoon pepper, radishes, and carrots. Set aside.
Cut open the baguettes all the way through (sandwich style).
On a sheet of parchment paper or waxed paper, shape the beef into 2 equal patties that are about ½ inch larger in area than the size of one baguette piece (burgers will shrink when cooked, so if you make them slightly larger, they will fit perfectly after cooking). Season the patties with additional pepper, if desired. Grill patties on high until desired doneness is reached, about 1-2 minutes per side for medium rare.
Meanwhile, add the baguette pieces to the grill, insides face down, away from a direct flame for about 30 seconds to 1 minute. Watch carefully so they don’t burn—you just want them very lightly toasted.
Place one bottom piece of baguette on each of two plates. Add a burger patty to each. Top each patty evenly with the cucumber, cilantro, and jalapenos.
Drain the carrots and radishes from the pickling liquid. Divide them evenly among the burgers. Drizzle each burger with sriracha and top with the baguette tops. Enjoy immediately.