Prep the chiles: In a small pot, cover the guajillo chiles with hot water.
Simmer for 5 minutes, then turn off the heat and let them soak until soft, about 10 minutes. Drain and set aside.
Blend the marinade: In a blender, add softened guajillos, chipotle in adobo, pineapple chunks and juice, vinegar, juice of 1/2 lime, garlic, onion, oregano, cumin, smoked paprika, coriander, cloves, brown sugar, 1 teaspoon salt, and a few grinds of pepper. Blend until smooth.
Marinate the chicken: Pat the chicken thighs dry.
Add them to a bowl or zip-top bag and pour in the marinade, reserving 1/4 cup for glazing later. Toss to coat. Marinate for at least 30 minutes and up to 12 hours in the fridge.
Preheat your cooking surface: Heat a large cast-iron skillet, grill pan, or outdoor grill over medium-high.
Lightly oil the surface.
Cook the chicken: Let excess marinade drip off, then cook the thighs 5–6 minutes per side, until charred in spots and cooked through. Internal temperature should reach 165°F (74°C).
Glaze and finish: Lower the heat to medium. Brush the reserved marinade over the chicken during the last minute on each side to caramelize.
Avoid heavy basting to prevent burning.
Rest and slice: Transfer to a cutting board and rest 5 minutes. Slice into thin strips or small chunks.
Warm tortillas and serve: Heat corn tortillas until pliable. Fill with chicken, diced onion, cilantro, a squeeze of lime, and a little chopped pineapple.
Add salsa if you like heat.