INGREDIENTS
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2 tablespoons canola oil, divided
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3 tablespoons chopped garlic
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2 sweet onions, such as Vidalia, chopped
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2 cups mushrooms, thinly sliced
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1/2 tablespoon kosher salt
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1/2 tablespoon freshly ground black pepper
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2 pounds flank steak
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Kosher salt
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Freshly ground black pepper
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1 (4-ounce) package baby spinach
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9 slices provolone cheese