"Think of vegetables for grilling in two categories," says chef Jean-Pierre Moullé. "Vegetables you have to cook a little before you grill them, and vegetables you do not have to cook before you grill them." A French native turned California surfer, Moullé runs the kitchen at Chez Panisse in Berkeley, which was among the very first American restaurants to install a wood-fired grill, in the 1970s (and kicked off the craze for fresh, local, seasonal produce).
When it comes to high-summer classics like eggplant, zucchini, summer squash, and peppers, Moullé advises they can go straight onto a hot grill – they have plenty of moisture to handle a grill's high heat – but slicing them in flat pieces helps. (Keep slices big and long, so they don't fall between the grill bars.) Tomatoes shouldn't be sliced at all, but just halved crosswise, along their equator. Then, simply toss with olive oil, salt, and pepper, and lay them flesh-side down on a medium-hot grill, long enough to soften up and sear.
Bring a huge pot of water to a boil; add 1 cup of salt per gallon. (Bigger pots prevent water from cooling once cold vegetables are dropped in.)
All but the very thinnest of asparagus should be peeled first, and all but the smallest leeks and onions should have their tough outer layers peeled off. Note that the outside burns long before the inside becomes tender for all three, which is why Moullé blanches them first.
Add vegetables to the water in small batches so your water never dips below the boiling point. Cook just until the tip of a sharp paring knife slips into the center without much resistance.
Remove vegetables to paper towels, let them cool and dry, and then toss them with olive oil, salt, and pepper. Shortly before serving, place directly over very hot coals, just long enough to get good sear marks and a wisp of smoke.