Prep: Rinse the rice until the water runs mostly clear, chop cilantro, and juice the limes.
In a bowl, toss the chicken thighs with olive oil, lime juice, garlic powder, onion powder, smoked paprika, cumin, salt, and optional chili powder; let marinate while rice cooks.
In a saucepan, bring water, olive oil or avocado oil, and salt to a boil over medium heat; add the rinsed rice and let it cook until the water starts to evaporate and small bubbles form.
Reduce heat to low and leave the rice uncovered for 2–3 minutes; then cover and cook on low for 5–7 minutes until fluffy; remove from heat and let sit covered for a few minutes.
Fluff the rice with a fork, then stir in chopped cilantro, fresh lime juice, and lime zest.
Heat a grill or grill pan over medium-high heat.
Grill chicken thighs for about 5–6 minutes per side until grill marks appear and the internal temperature reaches 165°F; let rest before slicing.
Spoon cilantro-lime rice into bowls, top with sliced grilled chicken, and add diced avocado, pickled onions, jalapeños, shredded lettuce, and salsa if using.
Serve with lime wedges on the side.