Whisk together olive oil, garlic, lime juice/zest, chili powder, cumin, oregano, salt, and pepper in a bowl.
Add chicken thighs and toss to coat evenly.
Cover and refrigerate for at least 15 minutes and up to 2 hours. (Longer than 2 hours in acidic marinades can start breaking down the meat too much.)
Heat your grill to medium-high. Lightly oil the grates.
Grill chicken thighs 5-6 minutes per side, or until internal temperature reaches 165°F.
Remove and let rest 5 minutes before chopping into bite-sized pieces.
Skillet Option: Heat 1 tablespoon oil in a large skillet over medium-high. Add marinated chicken and cook 6-7 minutes per side, until cooked through. Rest, then chop.
Make the Tomatillo-Habanero Sauce. Combine tomatillos, avocado, habanero, garlic, cilantro, lime juice, and salt in a food processor. Process until smooth. Taste and adjust salt or lime. Note: This is a raw, vibrant sauce - bright, creamy, and fiery.