In a nonreactive bowl (glass or stainless steel), combine the fresh lime juice, lemon juice, and orange juice. Whisk in kosher salt, granulated sugar, and black pepper until dissolved. Taste and adjust salt or acidity — the marinade should be bright and slightly salty.

Seafood and Vegetables

Prepare seafood

Pat the fish and shrimp dry with paper towels. Cut into uniform 1/2-inch dice so they 'cook' evenly in the citrus. Place the diced seafood in the bowl with the prepared citrus marinade, ensuring the pieces are submerged. Cover and refrigerate.

Marinate

Let the seafood marinate in the refrigerator until opaque and firm. For small dice (1/2-inch): about 20–30 minutes for fish, and 15–20 minutes for shrimp. If using a thicker cut or larger pieces, increase time but check often; avoid over-marinating to prevent a mushy texture.

Prepare vegetables

While the seafood marinates, very thinly slice the red onion and rinse briefly under cold water if you want to mellow the bite; drain well. Seed and dice the tomato, seed and finely chop the jalapeño, chop the cilantro, and dice cucumber if using. Combine these vegetables in a separate bowl.

Once the seafood is opaque and 'cooked' through, remove it from the refrigerator. Using a slotted spoon, transfer the seafood from the citrus into the bowl with the vegetables, reserving about 2–3 tablespoons of the marinade if you want a wetter ceviche. Discard excess marinade if desired.

Finish & Garnish

Gently fold the avocado into the ceviche along with the chopped cilantro and reserved marinade (if using). Add the extra-virgin olive oil and optional hot sauce. Taste and adjust seasoning with additional salt or a squeeze of lime if needed.

Let the assembled ceviche rest in the refrigerator 5–10 minutes for flavors to meld, then serve chilled with tortilla chips or on tostadas. Garnish each portion with a small drizzle of olive oil and a few cilantro leaves.