Place greens and 6 cups water in a 6-quart pot; bring to boil over high heat. Add 2 teaspoons each garlic salt, salt and pepper. Reduce heat to medium; cover and boil gently for 20 minutes. Drain into a colander, pushing on the greens with a spoon to squeeze out excess moisture.
While greens cook, heat oven to 375 degrees. Spray a 9- by 13-inch baking dish with non-stick cooking spray. Beat 6 eggs in a large mixing bowl, then whisk in milk and flour. Stir in cheese, bell pepper and 1 teaspoon each garlic salt and pepper.
Stir drained greens into egg mixture. Spread into prepared baking dish; bake 30 minutes.
Meanwhile, stir cornbread mix, corn and 2 eggs in a large bowl, mixing just enough to combine. Remove casserole from oven and spread cornbread mixture over top. Return to oven and bake 30 minutes longer, or until golden brown. Remove from oven and let stand 10 minutes. Cut into squares and serve.