Preheat oven to 350°. Remove and discard ribs from Swiss chard. Rinse with cold water; drain and coarsely chop.
Whisk together eggs and next 4 ingredients in a large bowl; stir in bread and half of cheese.
Sauté mushrooms and next 3 ingredients in hot oil in a large skillet over medium-high heat 8 minutes. Stir in Swiss chard, and sauté 2 minutes. Fold vegetable mixture into egg mixture. Pour into a lightly greased 11- x 7-inch baking dish. Sprinkle with remaining cheese.
Bake at 350° for 35 to 40 minutes or until center is set. Let stand 5 minutes.
Okra-Tomato Casserole: Omit mushrooms and Swiss chard. Substitute shredded Monterey Jack cheese for Parmesan cheese, 1 1/2 tsp. Cajun seasoning for salt, and green bell pepper for red bell pepper. Reduce pepper to 1/2 tsp. Prepare recipe as directed in Step 2, adding 2 Tbsp. chopped fresh flat-leaf parsley and 2 medium tomatoes, chopped, with bread. Proceed with recipe as directed, sautéing 2 cups sliced okra with onion 8 to 10 minutes in Step