Whisk together the tequila, lime juice, orange juice (if using), garlic, jalapeño, cumin, paprika, oregano, olive oil, and a pinch of salt and pepper in a large bowl to make the marinade.
Add the chicken thighs to the bowl and toss to coat evenly. Let the chicken marinate for at least 15 minutes at room temperature, or cover and refrigerate for up to 4 hours for deeper flavor.
Preheat your grill to medium-high heat. If you’re using a grill pan, heat it over medium-high on the stove.
Remove the chicken from the marinade, letting any excess drip off. Grill the chicken for about 5–7 minutes per side, or until the internal temperature reaches 165°F (74°C) and the surface is nicely charred.
Transfer the chicken to a cutting board and let it rest for 5 minutes. Slice thinly or chop into bite-sized pieces.
Warm the tortillas on the grill or in a dry skillet for about 20–30 seconds per side, until pliable and lightly charred.
Assemble the tacos by layering the grilled chicken on each tortilla, then adding your favorite toppings: cilantro, red onion, avocado, salsa, and a squeeze of fresh lime.
Serve immediately while hot and juicy, with extra lime wedges on the side for squeezing.