Slice the cucumber into thin rounds and place them in a non-reactive container. In a small saucepan, combine rice vinegar, salt, and sugar over medium heat, stirring until dissolved. Once combined, cool the mixture by adding ice. Pour the chilled pickling liquid over the cucumbers, seal the container tightly, and refrigerate for at least 4 hours to allow the flavors to meld.

In a medium saucepan, heat sesame oil over medium heat, then add the grated garlic and ginger. Sauté for about 2 minutes, or until fragrant, making sure not to burn them. Stir in the low sodium soy sauce, gochujang, brown sugar, and honey; bring this mixture to a gentle simmer. Combine water and cornstarch to form a slurry, then slowly stir it into the sauce until thickened, which takes around 5 minutes. Cool and store the BBQ sauce in the fridge.

In a mixing bowl, combine the mayonnaise, sriracha, sesame oil, and a splash of soy sauce. Whisk the mixture until smooth and well blended, ensuring the sriracha is fully incorporated for that delightful zing. Set aside the sriracha mayo in the refrigerator to let the flavors develop while you grill the chicken for your Korean BBQ Grilled Chicken Sandwich.

Prepare your grill by setting it up for two-zone cooking: one side at medium-high heat and the other at low heat. Season the chicken thighs generously with the Korean BBQ rub and lightly oil them to prevent sticking. Place the chicken on the direct heat side and cook for about 6-8 minutes per side, flipping frequently until nicely browned. Move the chicken to the indirect heat side and cook until its internal temperature reaches 165°F, which should take an additional 8-10 minutes.

Once the chicken reaches the proper temperature, remove it from the grill and brush a generous amount of the prepared BBQ sauce over each piece. Allow the coated chicken to rest for a few minutes, letting the sauce absorb into the meat.

Take your sandwich buns and spread a generous layer of the spicy sriracha mayo on each half. Place the grilled BBQ chicken on the bottom half of the bun, then pile it high with the tangy homemade pickles. Top it off with the other half of the bun, pressing down gently to hold everything together.