  XTE J1810-197 (PSR J1809-1943) was the first ever magnetar which was found to
emit transient radio emission. It has recently undergone another radio and
high-energy outburst. This is only the second radio outburst that has been
observed from this source. We observed J1810-197 soon after its recent radio
outburst at low radio frequencies using the Giant Metrewave Radio Telescope. We
present the 650 MHz flux density evolution of the source in the early phases of
the outburst, and its radio spectrum down to frequencies as low as 300 MHz. The
magnetar also exhibits radio emission in the form of strong, narrow bursts. We
show that the bursts have a characteristic intrinsic width of the order of
0.5-0.7 ms, and discuss their properties in the context of giant pulses and
giant micropulses from other pulsars. We also show that the bursts exhibit
spectral structures which cannot be explained by interstellar propagation
effects. These structures might indicate a phenomenological link with the
repeating fast radio bursts which also show interesting, more detailed
frequency structures. While the spectral structures are particularly noticeable
in the early phases of the outburst, these seem to be less prominent as well as
less frequent in the later phases, suggesting an evolution of the underlying
cause of these spectral structures.
