Rspec should already look recursively through the directory you named and find all tests. Note however, that it’s looking for files ending in _spec.rb. Maybe some of your files are not named correctly?
If you need to be more specific about which files it should find, you can also use the --pattern option. For example: rspec --pattern spec/requests/*_spec.rb. (Option --pattern is equal to -P. Taken from rspec --help)