Bring a large pot of water to boil. Remove from heat and add cornhusks. Weigh husks down with a plate or pot so they are totally submerged. Soak 30 minutes. Drain and rinse well with cold water.

While husks are soaking, heat oil in a large skillet over medium heat. Add onion, garlic, and chard stems. Cook until softened, about 6 minutes. Add zucchini and jalapeños and cook until softened, about 3 minutes more. Add chard leaves and cook until wilted, 2 minutes more. Cool mixture to room temperature, then stir in cotija. Taste and season with salt and pepper.

Whisk together masa harina and salt. Add lard and 2 cups hot water and stir to combine.

Sort cornhusks by size and set aside the largest cornhusks. Line a steamer basket with a few of the smaller husks. Place basket in a large pot and fill pot with water until it just reaches the husks. Tear remaining smaller husks into thin strips to make ties for the tamales.

One at a time, lay the larger corn husks out flat, smooth side up. Add about ¼ cup masa dough and smear over the husk until ¼-inch-thick or less. Add 2 heaping tablespoons vegetable mixture to each husk. Fold up the bottom of the husk then fold in the sides and top to make a bundle and seal the filling. Tie at the top with one or two husk strips. The tamale will look like a little cinched pouch. Repeat with remaining husks, masa, and filling. Place tamales in a steamer basket, cover, bring water to a boil, then gently simmer until dough is tender and puffed, about 40 minutes. Serve with hot sauce.