Expanding Access to Treatment Act This bill requires payment under Medicare to federally qualified health centers and rural health clinics that have health care practitioners who are newly certified to provide medication-assisted treatment. Specifically, a federally qualified health center or rural health clinic may receive payment for each health care practitioner who becomes certified on or after January 1, 2019, to prescribe or dispense methadone, buprenorphine, or suboxone (medications used to treat opioid-use disorders). The Centers for Medicare & Medicaid Services must set payments based on training costs for practitioner certification.