In a bowl, combine the lime juice, olive oil, onion, serrano and salt. Whisk and let sit for at least 15 minutes, or cover and refrigerate up to 12 hours.
When ready to serve, remove lime juice mix from the refrigerator. Slice the fresh scallops thinly and horizontally, up to 1/8” width. Spread on a platter. Whisk the lime juice sauce and pour in its entirety over the scallops, arranging so that the onion and chile are spread evenly throughout. Serve immediately.