I have been working in New Zealand since Dec '17 (Holiday work Visa for 1st year, Essential Skills Visa Jan '19-current). How do I file my taxes since I pay NZ taxes?

You will report your income under Less Common Income in the section Foreign Earned Income and Exclusion. Enter the income here and when the program asks if you would like to exclude the income answer "no, you know you do not qualify to exclude the income" (even though you may qualify - this will allow you to instead take credit for the taxes that you pay to New Zealand, which has a higher tax rate.) 

After you enter the income you will enter your New Zealand tax paid under Deductions and Credits, Estimates and Other Taxes Paid, Foreign Tax Credit.  Note that taxes paid on earned income are taxes on "General Category Income."