Clean and oil the grill grates. Grill the eggplant, covered, for 2-4 minutes, or until grill marks form on the bottom. Flip the slices; cook until grill marks form on the other side and the eggplant is mostly tender, about 2-4 minutes (it might not be cooked all the way through, and that’s okay!). Transfer the slices to a baking sheet or dish, and cover tightly with foil. Let sit for 5-10 minutes to steam, then uncover. Do Ahead: The grilled eggplant can sit out at room temperature for up to 6 hours, or it can be refrigerated for up to 3 days.