Heat grill to medium high. Combine radishes, asparagus and onions in a bowl, add olive oil, salt and pepper and toss well to combine. Add vegetables to a grill pan or mesh and place on the barbecue. Grill until a rich brown colour appears, tossing the vegetables from time to time. Assemble dressing while vegetables are grilling. Place grilled vegetables back into the bowl, drizzle with the dressing and top with pumpkin seeds and feta.