The rules for grilling vegetables are pretty much the same as those for grilling meat or seafood: Keep it hot. Keep it clean. Keep it lubricated. In other words, you want to start with a hot clean grate that you oil right before the food goes on. Heat your grill grate well, then scrub it with a stiff wire brush or scrape it clean with a wooden scraper. To oil it, fold or roll a paper towel into a tight pad, then clasp it in long-handled tongs. Dip it into a small bowl of vegetable or olive oil, and rub it across the grate in the direction of the bars. In addition to oiling the grate, this has the added advantage of giving the grate one last clean—and catching any stray brush bristles. Re-oil the grate as cooked vegetables come off and new ones go on. Note: When grilling smooth-skinned …