Bring a very large pot of water to a boil and add 1 tablespoon of salt. If the stems of the chard are tough, remove them entirely from the leaves and discard. (If the stems are tender, simply cut the stems off at the base of the leaves and discard.) Wash the leaves thoroughly. Immerse the chard in the boiling water and cook for 3 minutes exactly from the moment you get all the leaves in the pot. Drain immediately but don¿t squeeze out the liquid.
Warm 3 tablespoons of olive oil in a large (12-inch) saute pan. Add the sliced garlic and cook over medium heat for 30 seconds. Add the chard, sprinkle with 1 teaspoon salt and 1/2 teaspoon pepper, and saute for 3 minutes, tossing frequently with tongs.
Meanwhile, toast or grill 8 slices of bread. When they're nicely browned, rub one side of each slice of bread with a cut side of the halved garlic. Place 2 slices of toasted bread on each plate, garlic side up, and use tongs to distribute the chard onto the toasts. Sprinkle each serving with lemon zest, a squeeze of lemon juice, grated Parmesan cheese, and some fleur de sel. Drizzle the bruschetta with olive oil and serve warm. The liquid from the greens will be absorbed into the bread.