Preheat oven to 350 degrees Farenheit.
Place the shredded zucchini in a colander and sprinkle with 1 teaspoon salt. Allow the zucchini to drain for approximately 30 minutes. Squeeze the remaining liquid from the zucchini and place it on paper towels to blot dry. *Note - the zucchini needs to be very dry for this soufflé to rise well, so don't rush these drying steps.
In a large saucepot, melt 5 tablespoons of butter over medium/high heat. Add the corn, scallions, dried zucchini, 2 teaspoons salt, and pepper. Sauté together, occasionally stirring, for 3-5 minutes.
Stir 5 tablespoons of flour into the corn and zucchini mixture. Cook for at least 60 seconds, stirring constantly.
Slowly stir in the warm milk and continue to cook and stir until thickened.
Into the bowl with the egg yolks, add 2-3 tablespoons of the hot zucchini mixture, and stir to combine. *Note - this step is essential because it tempers the eggs so they don't curdle when you add them into the hot zucchini mixture. Don't omit this step!
Add the tempered egg yolk/zucchini mixture into the saucepot with the zucchini and corn. Stir well.
Remove the pot from the heat and stir in the shredded Swiss cheese.
Meanwhile, in the bowl of a stand mixer (or in a large bowl with a hand mixer), whisk the egg whites on high speed until stiff (approximately 3-5 minutes).
With a rubber spatula, gently fold ¼ of the egg whites into the zucchini/corn mixture until almost combined.
Gently fold in the remaining egg whites, being careful not to deflate the mixture.
Prepare a 2½ quart soufflé dish by buttering and lightly dusting with the remaining 1 tablespoon flour. Tap out the excess flour.
Pour the soufflé mixture into the prepared soufflé dish and bake in a preheated oven for 55-60 minutes or until the top is puffed and the center is browned and appears set.