There are many subtleties to translation involving word nuances and social and historical context and the social context. And neologisms in the original have their own difficulties. For the Italian word 'ecomostre', it seems to come from a portmanteau of the term 'ecological monstrosity' to describe a building that is large and ugly and also impacts surrounding natural situation badly.
To preserve the implications but not necessarily all the nuances of the Italian term, I suggest the best translation is:
ecological monstrosity
Just be as literal as possible. There's no equivalent single word in English.
Comments:
Just as Italian created the neologism, there's nothing stopping English from doing similarly, either by borrowing the word directly. Unfortunately 'ecomostrosity' would be unnatural in English, we'd really need to modify and add the 'n' back in to match the English 'monster' to make it a palatable English word.
But also, 'ecomonstrosity', while it could very well be a good English neologism (as suggested by TaliesinMerlin), it has already been used (though not enough to be included in dictionaries) and it means something different from the Italian. 'Ecomonstrosity' seems to be used by a small handful of authors to devote 'results of ecological disaster'.
Which is to say, if some journalist or TV pundit in English starts referring to brutalist architecture or dams that disrupt ecosystems as 'ecomonstrosities' then maybe that meaning will take off in English.
Which is to say if you really want a new word to become popular, get a New York Times op-ed article published with your word in the title.