Make the marinade. In a bowl, combine olive oil, garlic, lemon juice, red wine vinegar, cumin, smoked paprika, oregano, chili flakes (if using), salt, and pepper.
Whisk until smooth.
Marinate the chops. Pat the mutton chops dry. Add them to a large bowl or bag and coat with the marinade. Refrigerate for at least 1 hour and up to 12 hours. Longer marinating equals deeper flavor.
Prep the onions. Toss the sliced onions with 2 tablespoons olive oil and a pinch of salt and pepper.
Set aside.
Make the chimichurri. In a bowl, mix parsley, cilantro, garlic, shallot, red pepper flakes, olive oil, red wine vinegar, salt, and pepper. Taste and adjust with more vinegar, salt, or a squeeze of lemon. Let it sit while you cook to meld flavors.
Preheat the air fryer. Heat to 390–400°F (200–205°C) for 3–5 minutes. Preheating helps build a good crust.
Air-fry the onions first. Add the onions to the basket in a loose layer.
Air-fry at 380°F (193°C) for 6–8 minutes, shaking halfway, until softened and lightly caramelized. Remove and keep warm.
Cook the mutton chops. Lightly oil the air fryer basket. Remove excess marinade from the chops (don’t wipe completely clean).
Arrange in a single layer with space between. Air-fry at 400°F (205°C) for 8–12 minutes total, flipping at the halfway mark. Aim for an internal temp of 140–145°F (60–63°C) for medium; add or subtract time based on thickness.
Rest the meat. Transfer chops to a plate and rest 5 minutes.
This keeps the juices inside.
Plate and serve. Pile onions on a platter, place the chops on top, and spoon chimichurri over everything. Serve the extra sauce on the side.