Combine salmon and lime juice in a bowl, making sure fish is submerged. Cover with plastic wrap and refrigerate for 20 minutes.
Pour off all but 1 tbsp of the lime juice. Gently mix in avocado, onion, jalapeño, cilantro and salt. Garnish with more cilantro, if desired.
Buy best-quality seafood when it's to be eaten raw or undercooked.