Trim tough stem ends from Swiss chard. Cut stems crosswise into 1-inch pieces; cut leaves into 2-inch pieces, keeping stems & leaves separate.

In nonstick 12-inch skillet, heat oil over medium-high heat. Add onion and cook about 4 minutes or until onion begins to brown.

Add chard stems and cook, covered, 5 to 7 minutes or until tender.

Stir in raisins.

Add leaves to stems in batches, covering skillet after each batch; cook 7 to 10 minutes in total or until leaves are tender and wilted, stirring often.

Remove from heat, stir in capers.