Adjust oven rack to middle position and heat oven to 425 degrees.
Dry fish thoroughly with paper towels and season with salt and pepper.
Sprinkle very lightly with dusting of sugar (about 1/8 tsp) evenly over each side of fillet.
Heat oil in large ovensafe nonstick skillet over high heat until smoking.
Place fillets in skillet, sugared sides down, and press lightly to ensure even contact with pan.
Cook until browned, 1 to 1 1/2 minutes.
Using 2 spatulas, flip fillets and transfer skillet to oven.
Roast fillets until centers are just opaque and register 135 degrees (7-10 minutes).
Immediately transfer to serving plates and top with relish.
Relish: Process almonds, olives, garlic, and zest in food processor until nuts and olives are finely chopped, (10-12 one-second pulses). Transfer to bowl and stir in orange juice, vinegar, olive oil, and mint. Season to taste with salt and cayenne; serve spooned over fish.