Also, mightn’t the shrimp get overcooked and tough if it’s precooked, then sits in the oven at 350 degrees for another 35 minutes?
Depending on how finely it’s chopped is it possible for the shrimp to break down enough so the pieces are no longer tough? Perhaps there’s a chemical/enzymatic reaction between the shrimp and some of the other ingredients?
I may just add a bit of Old Bay Seasoning.
Or maybe some Zatarain’s!