In a medium bowl, toss together the pork, oil, garlic, and Cajun seasoning until meat is evenly coated; let stand for 15 minutes at room temperature.

Heat the gas grill to medium high (450 F) and oil the grates.

Meanwhile, assemble the kebabs: Thread the pork, grapes, onion, and peppers onto a skewer, alternating the ingredients to create an attractive pattern. Place on a tray. Repeat with the remaining ingredients to make 4 kebabs.

Grill the kebabs covered, until lightly charred underneath. Turn, cover, and grill 5 minutes more. Transfer kebabs to a platter and serve with lemon wedges.