The trick with appetizers is to avoid filling up your guests before the main course. Chicken Marbella, of which there are many variations, but most of which include oregano, red wine vinegar, olive oil, prunes, green olives, caper, and brown sugar, has a couple problems in the appetizer department.
First, you can often serve smaller portions of a dish and call it an appetizer. But most Chicken Marbella recipes we have seen call for quartered chickens or whole chicken breasts. Serving the dish in appetizer-sized portions will involve a lot of deboning or at least cutting, and the result is not likely to be lovely.
Second, a general rule of thumb is that foods that crunch stimulate the appetite, while soft foods satisfy the appetite. So if you want to serve something like Chicken Marbella for an appetizer, only serve a little, or follow it with a fairly light main course.