Ready time: 20 minutes
2 Spanish onions, peeled and sliced in half-inch rings
3 tbsp olive oil
Salt and freshly ground pepper
1 tbsp Dijon mustard
Preheat grill to medium-high. Brush onion rings with oil and season with salt and pepper. Grill 5 to 6 minutes a side, turning carefully with tongs. Check onions frequently, brushing with more oil as needed. Brush with mustard for the last 2 minutes of grilling.