Generally speaking, if you are a US person (citizen, green card holder, or resident alien) you must file a US income tax return that reports all your world-wide income and pays US tax, no matter where you actually live. This is tricky to do with Turbotax since it is officially limited to US residents. One way is to have someone in the US buy you a copy of the desktop program on CD to ship to you to install on your own computer. You can also buy the desktop version as a download as long as you have a US credit card with a US billing address. You may be able to use Turbotax Online but you will need a US credit card with a US billing address. If you are expecting a refund, the IRS will only do direct deposit to a US bank account, if you don't have one, they will mail a check to whatever address you specify.
On your US tax return, you can claim a deduction or credit if you also pay foreign income taxes on the same earnings (if Spain taxes your US retirement pay).
You can also claim an exemption from US tax on foreign earned income (income earned from working) if you are overseas at least 11 months. However, passive or unearned income (such as pension benefits) are not eligible for the exclusion and will always be subject to US income tax.
https://www.irs.gov/individuals/international-taxpayers/taxpayers-living-abroad
