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1
Rinse chiles and split open, discarding stems, seeds, and ribs.
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2
Heat a dry well-seasoned cast-iron skillet over moderate heat, then toast chiles in batches, turning them, about 30 seconds total.
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3
Transfer to a heatproof bowl and pour boiling water over them.
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4
Cover bowl and soak chiles, stirring occasionally, until softened, about 15 minutes.
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5
Reserve one fourth of soaking liquid, then puree chiles with remaining liquid in a blender until smooth (use caution when blending hot liquids).
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6
Pour pureethrough a fine sieve into a bowl, pressing on solids.
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7
Whisk in reserved soaking liquid.
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8
Toast bread crumbs in oil in a 2-quart heavy saucepan over moderate heat, stirring constantly, until pale golden, about 1 minute.
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9
Add garlic and oregano and cook, stirring, until fragrant, about 1 minute.
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10
Stir in chile puree, vinegar, and salt and simmer, stirring occasionally, until slightly thickened, about 25 minutes.
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11
Preheat oven to 350F.
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12
Cook onions in oil in a 12-inch heavy skillet over moderately low heat, stirring occasionally, until softened, about 20 minutes.
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13
Spoon half of chile sauce evenly over bottom of a lightly oiled 13- by 9-inch (3-quart) baking dish, then cover with 4 tortillas, overlapping slightly.
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14
Sprinkle tortillas evenly with one third of cheese, then half of onions and olives.
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15
Repeat layering with another 4 tortillas, another third of cheese, and remaining onions and olives.
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16
Top with remaining 4 tortillas, sauce, and cheese.
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17
Bake, uncovered, in middle of oven until cheese is melted and bubbling, about 25 minutes.
