Put the orange juice and thyme in a small saucepan, over medium heat and bring to a boil. Cook until reduced by half and becomes a syrup. Strain into a bowl, then add the honey and harissa, to taste.
Preheat the grill to medium.
Brush the fillets with oil on both sides and season with salt and pepper, to taste. Grill until slightly charred on both sides and just cooked through, about 4 minutes per side. Remove to a platter, drizzle with the sauce and sprinkle with olives and parsley.