"Onion" and "salsa" possess a similar structure:
both words consist of two identical
2-letter syllables and a distinct letter between them.
Apparently, there are more English words of similar form (12312).
Find as many as you can.
(In reply to Solution
by Dej Mar)
I hope we can all agree that the proposer of this puzzle has used the word "syllable" incorrectly (for digraph), though the "12312" shows what we all assumed he had in mind. If we allow "borrowed" legal terms, we could add "teste" (root in our words testimony and protest).