When Third Falcon opens this week in Fort Greene, a dish listed on the menu as “greens of the moment” may cause diners to roll their eyes with Greenmarket ennui, but it’s almost certainly unlike any other salad served in the city. It is, as the name suggests, made with whatever lettuces, herbs and flowers are in season — currently, a wide plate fanned and stacked with purslane, chrysanthemum greens, sesame leaf, basil, and fennel fronds — that are mixed...