Help with parallel_tests

[robroy05]

Greetings,
I'm looking for guidance on the proper usage of the parallel_tests gem.
The readme states to use the following format, but I am having trouble figuring out what options use to to make this work properly.
parallel_cucumber -o ' -f ReportPortal::Cucumber::ParallelFormatter'

If I run with:
parallel_cucumber features/featurefile.feature -f ReportPortal::Cucumber::ParallelFormatter I get the error shown below. I would assume there are additional options to provide to specify the output files, but I'm lost here. Can someone provide an example of the right command and how the output files should be structured?

.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:210:in stat': No such file or directory @ rb_file_s_stat - ReportPortal::Cucumber::Formatter (Errno::ENOENT) from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:210:in block in sort_by_filesize'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:210:in map!' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:210:in sort_by_filesize'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:63:in tests_with_size' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/test/runner.rb:42:in tests_in_groups'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/gherkin/runner.rb:87:in tests_in_groups' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/cli.rb:59:in block in run_tests_in_parallel'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/cli.rb:307:in block in report_time_taken' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests.rb:97:in delta'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/cli.rb:307:in report_time_taken' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/cli.rb:82:in run_tests_in_parallel'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/lib/parallel_tests/cli.rb:24:in run' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/gems/parallel_tests-2.31.0/bin/parallel_cucumber:9:in <top (required)>'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/bin/parallel_cucumber:23:in load' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/bin/parallel_cucumber:23:in

'
from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/bin/ruby_executable_hooks:24:in eval' from /Users/robert.aguirre/.rvm/gems/ruby-2.4.6/bin/ruby_executable_hooks:24:in '