Preparation

• Prepare a medium (350°F to 375°F) gas or charcoal grill fire. (Alternatively, heat a grill pan over medium heat.)
• Using a fork, mash the avocado with 2 Tbs. of the cilantro, the lime juice, 1/2 tsp. salt, and a few grinds of pepper in a medium bowl; the mixture should be chunky. Set aside.
• Oil the grill grate. Pat the crabs dry with paper towels and then brush them on both sides with 2 Tbs. of the oil. Season all over with salt and pepper. Grill, turning once, until lightly charred on the outside and an instant-read thermometer inserted in the center reads about 145°F, about 5 minutes total. Transfer to a large plate or baking sheet.
• Meanwhile, toss the scallions with the remaining 1 Tbs. oil. Arrange the scallions perpendicular to the grill grate and cook, turning once, until browned and wilted, about 6 minutes. Transfer to a cutting board and cut crosswise into bite-size pieces; sprinkle lightly with salt.
• Grill the tortillas, flipping once, until warm, soft, and lightly charred in spots, about 1 minute per side. Stack the tortillas in a kitchen towel.
• Top each tortilla (or doubled tortillas) with some of the avocado mixture, some of the scallion, 1 crab, and the remaining cilantro. Serve with lime wedges.