  We present a spatially resolved spectroscopic study for the metal poor HII
galaxy J084220+115000 using MEGARA Integral Field Unit observations at the Gran
Telescopio Canarias. We estimated the gas metallicity using the direct method
for oxygen, nitrogen and helium and found a mean value of
12+$\log$(O/H)=$8.03\pm$0.06, and integrated electron density and temperature
of $\sim161$ cm$^{-3}$ and $\sim15400$ K, respectively. The metallicity
distribution shows a large range of $\Delta$(O/H) = 0.72 dex between the
minimum and maximum (7.69$\pm$0.06 and 8.42$\pm$0.05) values, unusual in a
dwarf star-forming galaxy. We derived an integrated $\log$(N/O) ratio of
$-1.51\pm0.05$ and found that both N/O and O/H correspond to a primary
production of metals. Spatially resolved maps indicate that the gas appears to
be photoionized by massive stars according to the diagnostic line ratios.
Between the possible mechanisms to explain the starburst activity and the large
variation of oxygen abundance in this galaxy, our data support a possible
scenario where we are witnessing an ongoing interaction triggering multiple
star-forming regions localized in two dominant clumps.
