De Cunha opened the scoring in the 27th minute from the left with a low shot into the far post.
Como had their second ten minutes later as Patrick Cutrone produced an almost identical finish from the right.
Alessandro Gabrielloni made it 3-0 in the 59th with an effort that should have easily been dealt with by Spezia keeper Jeroen Zoet.
De Cunha put the icing on the cake just four minutes later when he finished a cutback from Marco Sala.
Como sit third, equal on points with Venezia. Spezia are second last and in trouble.
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