Arrange 2 of the tortillas on a work surface and top with the ham, tomatoes, cheese, coriander and some salt and pepper. Top with the remaining tortillas, pressing down firmly. Cook one of the quesadillas on the flat plate of a hot gas barbecue for 2—3 minutes, turning halfway through, until each side is charred and crisp. (For a charcoal barbecue, use a preheated ridged grill pan instead.) Serve as below, then cook the second quesadilla.
Transfer the quesadillas to a board, cool for a second or two and then cut into wedges to serve.