Tuna in Escabeche

Name: Tuna in Escabeche
Ingredients: 3 Tbs. olive oil; 1 1/2 lb. (750 g) albacore or yellowfin tuna fillet, about 1 inch (2.5 cm) thick, cut into 6 to 8 pieces; 1 red bell pepper, seeded and thinly sliced; 1/2 red onion, thinly sliced; 1 cup (8 fl. oz./250 ml) dry white wine; 3/4 cup (6 fl. oz./180 ml) sherry vinegar; 2 garlic cloves, crushed; 1/2 tsp. black peppercorns; 1 tsp. grated orange zest; 1 tsp. sugar; 1/2 tsp. red pepper flakes; Kosher salt; 1/2 cup (2 1/2 oz./75 g) pitted olives