Prep the pan. Lightly oil a 9x13-inch baking dish or set up your slow cooker.
Preheat oven to 400°F if baking.
Layer the base. Scatter the sliced onion in the bottom of the dish or slow cooker. Add the minced garlic.
Season the chicken. Pat chicken dry. Sprinkle both sides with salt, pepper, cumin, chili powder, and smoked paprika.
Dump and coat. Place the chicken over the onions.
Pour the salsa verde evenly on top, turning the chicken once to coat.
Cook it. Oven: Bake uncovered for 22–28 minutes (breasts) or 28–35 minutes (thighs), until the thickest part reaches 165°F.
Slow cooker: Cook on LOW for 4–5 hours or on HIGH for 2–3 hours, until tender.
Finish with lime. Squeeze lime juice over the chicken, then rest for 5 minutes.
Shred or slice. For tacos and bowls, shred the chicken in the pan so it soaks up the sauce. For plates, slice and spoon sauce over top.
Serve. Top with cilantro and your favorite add-ons. Taste and add a pinch more salt or a splash of lime if needed.