## [Wolfram Language (Mathematica)], <s>52</s> 45 bytes

    ToExpression@*StringReplace[{"["->"Prime[1"}]

[Try it online!][TIO-jb5310rs]

[Wolfram Language (Mathematica)]: https://www.wolfram.com/wolframscript/
[TIO-jb5310rs]: https://tio.run/##y00syUjNTSzJTE78H1CUmVei4KCloPE/JN@1oqAotbg4Mz/PQSu4BCiTHpRakJOYnBpdrRStpGunBFSdmxptqFQb@19TQd9BoZpLQUEpOlZJB0hGx0LoWBgfKAATgcmBJOGqEPqQ9MJ0QQyGCaAKgw0EiyALgVWBBWGycEkIiIUCDD0QmWiIdbGxGE7ACZW4av8DAA "Wolfram Language (Mathematica) – Try It Online"

Input uses brackets.

Transforms the input into a Mathematica expression that computes the result. We do this simply by replacing `[` with `Prime[1`. This works because concatenation *is* multiplication in Mathematica.