How to Make It
In a large skillet, heat 2 tablespoons of the canola oil. Add the onion, garlic, bay leaf, pickling spice mix and peppercorns and cook over moderate heat, stirring occasionally, until the onion is softened but not browned, 7 to 8 minutes. Transfer the onion mixture to a medium bowl and let cool for 15 minutes.
Meanwhile, season the fish with salt. In a large nonstick skillet, heat 2 tablespoons of the canola oil until shimmering. Add half of the fish and cook over moderately high heat until golden and just white throughout, about 3 minutes per side. Using a slotted spoon, transfer the fish to a large ceramic or glass baking dish. Repeat with the remaining 2 tablespoons of canola oil and the remaining fish.
Prepare an ice bath. Score an X on the bottom of the tomato. In a medium saucepan of boiling water, blanch the tomato just until the skin starts to wrinkle, about 30 seconds. Using a slotted spoon, transfer the tomato to the ice bath to cool. Slip off the skin and halve the tomato crosswise. Gently squeeze out the seeds. Cut the tomato into 1/4-inch dice.
Roast the jalapeño directly over a gas flame or under a preheated broiler, turning, until charred all over. Let cool. Using a paper towel, rub off the skin; discard the stem and seeds. Thinly slice the jalapeño.
Stir the tomato and jalapeño into the onion mixture along with the olive oil, lime juice, orange juice, olives, red pepper, capers and parsley. Spoon the escabèche topping over the fish, cover with plastic wrap and refrigerate for 24 hours.
When ready to serve, let the escabèche stand at room temperature for 45 minutes. Fold in the avocado and season with salt. Spoon the escabèche into bowls and garnish with bay leaves.