Roughly chop 1/2 onion and place in a blender with the chili powder, 1 1/2 teaspoons salt, the oregano, cumin, cloves and garlic. Puree, adding about 1/3 cup water to make a thick paste.
Slice the remaining 1 1/2 onions into thin rings and place in a bowl with the chili puree and pork; toss to coat.
Lightly brush a large cast-iron skillet or grill pan with vegetable oil and place over high heat until almost smoking. Place 4 pork chops in the skillet and surround with half of the onions. Cook until the pork starts to blacken on the outside and is cooked through, about 4 minutes per side. Repeat with the remaining pork chops and onions. Serve with rice, if desired.