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1
Preheat the oven to 400 F; Spray a 13-by-9-inch baking pan with cooking oil spray; Set aside.
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2
Stack the tortillas on a cutting board, and slice through them lengthwise into 3 strips each (The strips will not be uniform because of their circular shape; This is OK) Set aside.
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3
Pour the corn and black beans into a colander, and rinse with warm tap water to begin defrosting the corn and rinse the beans; Set aside to drain.
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4
In a small bowl, stir together the tomatoes with their juice, the tomato sauce, chili powder, cumin, garlic powder and sugar; Spoon about half of the sauce into the bottom of the dish; Cover the sauce with 5 of the tortilla strips (it's fine if they overlap somewhat).
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5
Break the egg into a medium-size mixing bowl, and beat with a whisk or fork until foamy; Add the sour cream and 1 cup of the cheese; Stir to mix well; Spoon half of the sour cream mixture evenly over the tortilla layer and spread it out with the back of a spoon; Scatter half of the corn and black beans over the sour cream mixture.
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6
Place 5 more tortilla strips evenly over the corn and black bean layer; Top with the remaining sour cream mixture, and the remaining black beans and corn; Place the remaining tortilla strips over the dish; Pour the remaining tomato sauce mixture over the tortillas, and spread it evenly with the back of a spoon to moisten all of the tortilla strips.
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7
Cover the dish with foil, and bake for 30 minutes, or until hot and bubbly.
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8
While the dish bakes, rinse and trim the green onions; Slice the green onions thinly, using all of the whites and enough of the tender green tops to make 1/2 cup; Set aside.
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9
If using the black olives, drain them well, and set aside.
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10
After baking lasagna, scatter the green onions and olives, if using, evenly over the dish; Return the dish to the oven, uncovered, for 5 more minutes.
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11
Remove the dish from the oven, and scatter the remaining cup of Mexican cheese evenly over the dish.
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12
Return the dish, uncovered, to the oven, and bake until the cheese melts, about 3 minutes.
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13
Remove the lasagna from the oven, and let it stand 10 minutes; Slice into squares and serve.
