1. Preheat oven to 245 °C (475 °F). Place rack in centre of oven. Line a baking sheet with aluminum paper (or use a reusable baking mat).
2. Place water, chili sauce, cornstarch, cocoa and chipotle pepper into immersion blender container. Blend until smooth and set aside.
3. Halve and thinly slice onion. Place half the onion on baking sheet and place the other half in a small bowl.
4. Squeeze lime over bowl, mix and set aside.
5. Peel pineapple and remove core.
6. Cut pineapple and fish into cubes. Place on baking sheet.
7. Pour sauce over fish and pineapple cubes. Mix to coat well.
8. Bake for 18 minutes or until fish flakes easily with a fork.
9. Meanwhile, remove cilantro leaves and crumble feta.
10. Garnish tostadas with fish, feta, lime-marinated onions and cilantro. Sprinkle with chili seasoning, if desired, and serve.

This recipe is best assembled just before serving, but the fish mixture will keep for 3 days in the fridge.

Chef’s secrets:

• For the chipotle: these smoked, dried jalapeno peppers are coated in tomato sauce and blend beautifully with Mexican dishes. You can find them in most grocery stores, in the Mexican product aisle or in the sauces and condiments aisle. You will likely not use a full jar, so you can freeze the rest in 15 mL (1 tbsp.) servings. If you can’t find this ingredient or prefer a less spicy version, chipotle can be replaced with 80 mL (⅓ cup) marinated roasted red peppers.
• For the pineapple: at the grocery store, look for deals on fresh peeled pineapple. They are sometimes cheaper than whole pineapples, and most of the work is already done!