Instructions

1. Juice 3 to 3 1/2 medium limes into a large bowl until you have 1/4 cup. Cut 1/2 medium lime into wedges for serving. Finely grate 2 garlic cloves into the bowl.
2. Add 2 tablespoons of the vegetable oil, 2 teaspoons kosher salt, 1 teaspoon ground cumin, and 1 teaspoon chili powder, and stir to combine. Add 2 pounds boneless, skinless chicken thighs and turn to coat. Let sit for at least 10 and no longer than 15 minutes.
3. Meanwhile, if using an outdoor grill, heat to direct, medium-high heat (about 400ºF).
4. Finely chop 1/2 small red or white onion until you have 1/2 cup. Finely chop fresh cilantro leaves and tender stems until you have 1/2 cup. Place both in a small bowl and stir to combine.
5. If cooking on the stovetop, heat a grill pan over medium-high heat for about 5 minutes. Drizzle the remaining 2 tablespoons vegetable oil onto the pan. Add the chicken thighs and let cook until golden-brown and charred in spots on the bottom, about 5 minutes. Flip and continue to cook browned on the second side and the internal temperature registers at least 165ºF, 4 to 5 minutes more.
6. If cooking on an outdoor grill, remove the chicken from the marinade and brush with the remaining 2 tablespoons vegetable oil. Scrape the grill grates clean if needed. Place the chicken on the grill, cover, and cook until charred in spots, cooked through, and golden brown all over, about 15 minutes total.
7. Transfer the chicken to a clean cutting board and let rest for 5 to 10 minutes. Meanwhile, prepare the toppings.
8. Using a mandolin or sharp knife, thinly slice 1 bunch radishes (save the greens for another use). Halve, pit, and peel 1 medium avocado. Thinly slice the halves and cover with a damp paper towel if not using immediately.
9. Warm 10 to 12 flour or corn tortillas one at a time by holding them directly over a medium flame on a gas stove or outdoor grill, or in a skillet over medium heat on an electric stove, flipping occasionally, until charred in spots and pliable. (Alternatively, wrap the stack of tortillas in a damp paper towel and microwave until warm, 20 to 25 seconds.) Stack together and wrap in a clean kitchen towel or aluminum foil to keep warm.
10. Coarsely chop the chicken into 1/2 to 1/4-inch pieces. Transfer to a bowl, add half of the onion and cilantro mixture, and toss to combine.
11. Assemble the tacos one at a time: Top 1 of the tortillas with 1 scant tablespoon sour cream and 1 avocado slice. Add 1/3 cup of the chicken mixture and top with more of the cilantro and onion mixture if desired. Drizzle with salsa verde and top with a few radish slices. Serve with the lime wedges.