This is really an appetiser, but I've been known to just make a platter of them for a summer lunch. Too good for words, and equally simple.
Scrape the gills off the underside of 4 large portobello mushrooms. Brush each side lightly with olive oil, then grill for about 4-5 minutes each side.
While they grill, crush a clove of garlic, tear up a 1/4 cup basil leaves, and combine in a small bowl with 1-2 Tbsp olive oil, a dash of salt, and some freshly ground pepper.
When the caps come off the grill, place them on a plate (upside down) and spread them with the basil and garlic mixture. Serve immediately (warm).