Place the chicken thighs into a bowl. In a mortar and pestle pound together the garlic and ¾ teaspoon salt until a paste forms. Add olive oil, citrus juice and crumbled oregano, mix until combined. Pour the marinade over the chicken and toss to coat, marinate for at least 30 minutes up to overnight.
Heat a grill or grill pan to medium high heat. Place the chicken on the grill being careful to not over crowd the grill or grill pan. Cook without moving for 3-4 minutes, the chicken should be golden and fragrant. Flip the chicken over and cook for another 3-4 minutes or until it feels firm when pressed in the thickest part of the thigh. Serve with black beans and rice.