Remove the pith from the lime and finely dice the flesh of the lime.
In a small bowl, lightly mash the lime with the fork to release some of the lime juice and then stir in the chopped jalapeño pepper (optional), cucumber, onion, cilantro, and ½ teaspoon of salt. Set aside and let the salsa ingredients marinate together.
Heat 1 Tablespoon of olive oil in a skillet over medium heat.
Season the salmon filets with a the remaining salt and ¼ teaspoon of pepper.
Sauté the salmon, skin side down, until golden brown, about 7-8 minutes.
Carefully flip the salmon and continue to cook until the flesh is opaque and flakes easily when a fork is inserted and slightly turned...about 4 more minutes.
Transfer salmon to plates and spoon cucumber salsa over top. Serve immediately!