Heat oven to 300ºF. Line 2 half-sheet pans with parchment paper and set aside.
Wash and thoroughly dry the greens. Tear the larger leaves into 1- to 2-inch strips.
Lay the greens in a single layer on the half-sheet pans, spritz lightly with the olive oil, and sprinkle with the salt.
Bake until the greens are dry and have darkened slightly, 15 to 20 minutes. Remove immediately from the pan on the parchment and transfer to a serving dish. Repeat with any remaining greens. Serve immediately, or store in a brown paper bag for up to 3 days.