In a large bowl, whisk together granulated sugar, black pepper, five spice powder, sesame oil, soy sauce, fish sauce, honey, minced garlic, and shallots until well combined. Add the boneless, skinless chicken thighs and coat thoroughly. Cover and refrigerate for at least 4 hours, preferably overnight.

Heat a large skillet over medium-high heat and add a splash of oil. Remove the chicken from the marinade (reserving marinade) and sear the thighs for about 3 minutes each side until golden brown.

Reduce heat to low and add reserved marinade to skillet. Cover and simmer for 10 minutes. Uncover, increase heat to medium-high, and cook for an additional 5 minutes.

Transfer chicken to a cutting board, let rest for a few minutes, and then slice into thin strips.

Slice baguette lengthwise and lightly toast in a preheated oven at 350°F (175°C) for about 5 minutes.

Spread mayonnaise inside the toasted baguette. Layer sliced chicken, pickled vegetables, cucumber slices, jalapeños, and cilantro.