How to use conversation.process response in a script to control entities

As so many, I am playing around - mostly for fun - trying to use OpenAI conversation to actually control entities. It is not too difficult to come up with (or find with google) a prompt that provides some information about entities and entity states and that will return a json formatted HA service call.

When running conversation.process using the official OpenAI Conversation service, this would for example give me the below response. I understand the reason why the response is only in the speech field (and that is fine).

response:
  speech:
    plain:
      speech: >-
        {"service": "light.turn_off", "entity_id": "light.light_living_room_local"}
      extra_data: null
  card: {}
  language: en
  response_type: action_done
  data:
    targets: []
    success: []
    failed: []
conversation_id: xxxxx

What I would like to do now, is to run this in a script and use the response.speech.plain.speech variable to actually execute the service call. I got the feeling this should be trivial, but I just can’t seem to figure out a way to do it. Does someone have an idea?