For the pickled veggies: julienne the carrots and daikon radish, slicing them into planks, and then matchstick shapes.
In a small pot over medium heat, add the rice vinegar, water, sugar, and salt. This is your pickle brining liquid. Bring it to a boil and then remove the pot from the heat.
Add the carrots and daikon radish to a container and pour over the pickle brine. Store these in a covered container in the refrigerator overnight.
For the pork belly: add the garlic, soy sauce, brown sugar, sliced chili, fish sauce, and vegetable oil to a small pot over medium heat and bring the liquid to a boil. This is your marinade for the pork belly. Add the marinade and the pork belly to a zip-top bag or sealed container and store in the fridge.
Marinate the pork belly in the refrigerator overnight or for up to 24 hours.
The next day: when you are ready to cook, preheat your oven to 300 degrees F (148 C).
Remove the pork belly from the marinade and dry the skin very well with paper towels. Cut shallow slices in the skin about a quarter inch apart, just cut through the skin and no deeper.
Place the pork belly on a sheet pan or baking dish, skin side up, and cook for 2.5 hours.
After 2.5 hours, remove the pork belly from the oven and raise the heat on the oven to 500 degrees F (260 C).
Move the pork belly to a wire rack, set it over a lined baking sheet, and place it in the oven for an additional 25 to 30 minutes. This is meant to crisp up the skin.
Remove the pork belly from the oven and allow it to cool for at least 30 minutes before slicing. If you want thinner slices, you can cool the pork belly in the refrigerator for 3 or 4 hours until the meat is firmer.
Sandwiches assemble: when it's sandwich time, slice your two 6 to 8-inch pieces of French bread two-thirds of the way through. Don't cut the bread all the way through, leave the backside to serve as a bread hinge.
Place a medium pan over medium-high heat. Add enough slices of pork belly for your two sandwiches and sear the pork for 4 minutes per side to warm it up and add some extra texture from the searing.
Spread the mayonnaise and sriracha sauce into the interior of the bread.
Add slices of pork belly to the bread.
Next, add slices of cucumbers and jalapenos.
Top with pickled carrots and daikon radish and cilantro leaves.
Top the sandwiches with more sauce if desired. Serve and enjoy.