How to plot two maps, one on top of another with imshow and geopandas

Question

I'm using this code:

import cartopy.crs as ccrs

ax = plt.axes(projection=ccrs.UTM(zone='36N'))

#fig,ax = plt.subplots(1,figsize=(10,10))
ax.imshow(region_mask, cmap='RdYlGn_r')
upoly.plot(ax=ax)
plt.show()

The outcome is the following:

I'm trying to combine these two images:

upoly.plot()

and ax.imshow(region_mask)

This is what the region mask data looks like

array([[ 288.33252,  521.2652 ,  780.06146, 1066.1105 ,  253.47798,
           0.     ,    0.     ,    0.     ,    0.     ,    0.     ,
           0.     ],
       [ 498.93793,  976.3347 , 1550.9442 , 1585.4607 ,  716.0737 ,
         236.821  ,  232.02997,    0.     ,    0.     ,    0.     ,
           0.     ],
       [   0.     ,  947.0323 , 1582.3849 , 1585.4637 , 1585.4623 ,
         703.5349 ,  229.36992,    0.     ,    0.     ,    0.     ,
           0.     ],
       [   0.     ,    0.     ,  966.4486 , 1585.4662 , 1563.7642 ,
        1281.5676 ,  531.6347 ,  236.73157,  227.37653,    0.     ,
           0.     ],
       [   0.     ,  843.1128 , 1314.082  , 1578.0651 , 1429.404  ,
        1172.7765 , 1172.7769 , 1008.69507,  327.10162,    0.     ,
           0.     ],
       [   0.     ,  743.6814 , 1176.5321 , 1553.9138 , 1442.5048 ,
        1172.7786 , 1172.7787 ,  837.7045 ,  333.35812,  227.37726,
           0.     ],
       [   0.     ,    0.     ,  897.54974, 1535.5205 , 1471.0431 ,
        1172.7808 , 1172.7809 , 1167.3474 , 1172.6633 ,  913.6754 ,
         249.76035],
       [   0.     ,  546.41644, 1019.9813 , 1535.5228 , 1481.7703 ,
        1172.7825 , 1172.7826 , 1031.3147 ,  602.0616 ,  852.7764 ,
           0.     ],
       [   0.     ,  930.4068 , 1494.0599 , 1535.5255 , 1499.4604 ,
        1149.757  ,  629.6995 ,    0.     ,    0.     ,    0.     ,
           0.     ],
       [   0.     , 1107.7336 , 1535.528  , 1268.1655 , 1194.783  ,
         638.2148 ,    0.     ,    0.     ,    0.     ,    0.     ,
           0.     ],
       [   0.     ,    0.     ,  846.92377,    0.     ,    0.     ,
           0.     ,    0.     ,    0.     ,    0.     ,    0.     ,
           0.     ]], dtype=float32)

If you need more information please let me know.