Place each chicken cutlet between two sheets of plastic wrap or parchment paper. Using a meat mallet or rolling pin, pound the chicken to an even ⅓” (8mm) thickness.

In a large bowl, whisk together the water and salt until the salt is completely dissolved. Add the lemon, garlic, red pepper flakes, black peppercorns, and rosemary. Add the chicken, making sure the cutlets are fully submerged. Cover and refrigerate for 3–4 hours.

In a medium saucepan over medium heat, add the guanciale and olive oil. Cook, stirring occasionally, until the guanciale is golden brown and crisp and the fat has rendered, about 5–8 minutes. Using a slotted spoon, transfer the guanciale to a bowl or tray, leaving the rendered fat and oil in the saucepan.

Add the garlic to the rendered fat and cook, stirring often, until softened and lightly golden, about 1–2 minutes.

Add the gochujang and cook, stirring constantly, until it darkens slightly, begins to caramelize, and becomes fragrant, about 1–2 minutes.

Add the sugar and red pepper flakes, then pour in the crushed tomatoes and stir to combine. Season lightly with salt, keeping in mind that the guanciale and Pecorino Romano will add additional salt later.

Bring the sauce to a gentle simmer. Tie the thyme together with kitchen twine, if desired, and add it to the sauce. Reduce the heat to medium-low and simmer, stirring occasionally, until the sauce has slightly thickened and coats the back of a spoon, about 15–20 minutes.

Meanwhile, finely chop the reserved crispy guanciale by hand or pulse it briefly in a food processor. Once the sauce has thickened, remove and discard the thyme. Fold in the chopped guanciale, adjust the seasoning to taste, and keep warm over low heat until ready to assemble.

Remove the chicken from the brine and discard the brine and aromatics. Rinse the cutlets briefly under cold water, then thoroughly pat dry with paper towels.

Set up a breading station with three shallow bowls or ¼ sheet trays. Add the flour to the first. In the second, whisk together the eggs, water, salt, and black pepper until smooth. Add the panko to the third.

Working one at a time, dredge each cutlet in the flour, shaking off any excess. Dip into the egg mixture, allowing the excess to drip away, then thoroughly coat in the panko, gently pressing the breadcrumbs onto the chicken to ensure an even coating. Transfer to a wire rack or sheet tray and repeat with the remaining chicken.

Fill a large cast-iron skillet with about 1” (2.5cm) of neutral oil and heat to 350°F (177°C). Working in batches to avoid overcrowding the pan, carefully lower the breaded cutlets into the hot oil. Fry until golden brown and crisp on the first side, about 2–3 minutes. Add a sprig of rosemary to the oil during the final 30–60 seconds before flipping.

Flip the chicken and continue frying until deeply golden and the internal temperature reaches 165°F (74°C), about 2–3 minutes more. Transfer the chicken to a wire rack set over a sheet tray and season lightly with salt while hot. Transfer the fried rosemary to the rack as well. Allow the oil to return to 350°F (177°C) before frying the remaining cutlets.

Preheat the broiler to high with a rack positioned about 6” (15cm) below the heating element.

In a large bowl, combine the low-moisture mozzarella, full-fat mozzarella, and Pecorino Romano. Gently toss until evenly combined.

Transfer the fried cutlets to a foil-lined baking sheet. Top each cutlet with about 4 oz (120g) of sauce, followed by a generous handful of the cheese mixture. Broil until the cheese is completely melted, bubbling, and beginning to brown in spots, about 2–4 minutes. Watch closely to prevent burning.

Transfer the chicken to serving plates. Garnish with thinly sliced chives, if desired. Serve immediately and enjoy!