2 3/4 pounds curly mustard greens (2 to 3 bunches), stems and coarse ribs discarded
4 bacon slices, cut crosswise into 1/2-inch pieces
3 tablespoons olive oil
1 teaspoon minced canned chipotle chiles in adobo
1/2 teaspoon salt
Coarsely chop greens, then cook in 2 batches in a 6- to 8-quart pot of boiling salted water , uncovered, stirring occasionally, until wilted and tender, about 5 minutes. Transfer with a slotted spoon to a large bowl of cold water to stop cooking. Drain greens in a colander, pressing gently to release excess moisture.
Cook bacon in a 12-inch heavy skillet over moderate heat, stirring, until crisp, 4 to 5 minutes. Transfer with a slotted spoon to paper towels to drain, reserving fat in skillet. Add oil, chipotle, greens, and salt to fat and cook, stirring occasionally, until heated through, 2 to 3 minutes. Transfer to a serving dish and sprinkle with bacon.