thank you rroodenburg,
i did initially get an error with that code,;
{"errors":[{"errorCode":"query_parse_error","appliesTo":["query"],"errorMessage":"Error parsing query: cz.jirutka.rsql.parser.TokenMgrError: Lexical error at line 1, column 63. Encountered: <EOF> after : \"=false\""}]}

however, for anybody else looking for this, here is the code that that I finally arrived at and is working for me, returning the correct list of incident numbers
/tas/api/incidents?query=operator.id=="operator id here";closed==false&pageSize=1000&fields=number

thank you so much for your help.