Greens wilt because they lose turgor pressure—essentially, the water inside their cells has evaporated. You can fix this through osmosis.
The Ice Water Shock
Submerge the wilted greens in a large bowl of ice water. Add a squeeze of lemon juice (the acid helps strengthen cell walls). Let them soak for 15-30 minutes.
The Results
The cells will drink up the cold water, restoring their internal pressure and making the leaves crisp and crunchy again.