Bring a medium saucepan of water to a boil. Halve the chard leaves lengthwise and remove the thick ribs and stems. Cut the ribs and stems into 1/4-inch dice and transfer 3/4 cup to a large bowl; discard the rest. Blanch the chard leaves in the boiling water until just wilted, about 10 seconds. Transfer the chard leaves to a bowl of ice water to cool, then drain and pat dry.
Bring the water in the saucepan back to a boil. Add the nettles and blanch for 1 minute (10 seconds if using spinach). Drain and refresh in ice water, then drain and squeeze dry. Coarsely chop the nettles and add to the chard stems, along with the parsley, sorrel, chives, zucchini, lovage, thyme, garlic, Pecorino, bread crumbs and 4 tablespoons of the olive oil. Season with salt and pepper and gently toss.
Make a slit in the side of each zucchini blossom and snap off the pistils in the center. Spread the chard leaves on a work surface and pat completely dry. Spoon an equal amount of filling on each leaf. Press lightly and season with salt and pepper. Tightly roll up the chard leaves cigar-style. Stuff the chard rolls into 12 of the zucchini blossoms. Carefully fit these into the remaining 12 blossoms, overlapping the petals to seal.
Arrange the blossoms, seam side down, in a large skillet in a single layer. Add 1/2 cup of water and the remaining 2 tablespoons of olive oil and bring to a simmer. Cover tightly and cook over moderately high heat until just tender when pierced with a knife, about 10 minutes. Uncover and cook until the liquid is reduced to 3 tablespoons, about 2 minutes longer. Transfer the zucchini blossoms to a platter and drizzle the pan juices on top.