I don’t know if I’m understanding your question. What I recommend doing is to:
determine significant environmental aspects and determine which need to be part of a monitoring and measuring plan
determine monitoring and measuring requirements based on compliance obligations
Based on 1 and 2 develop a monitoring and measuring plan. Some indicators are explicit requirements from compliance obligations with specifications and frequency defined. Some indicators are determined by the organization and can be absolute or relative. For example, water or energy consumption per unit amount of output.
Together with evaluation of environmental performance I recommend doing the evaluation of action plans progress.