All fights for justice and the end of oppression interrelate in certain ways, both symbolically and in reality. For example, the fight against class discrimination and the fight against racism are interrelated both through historical origins and present systematic similarities and intersections. The oppression of women is historically tied to the exploitation of nature.
Similarly environmental exploitation and fight for justice intersects with mentalism and mental health justice.
For one, the exploitation of nature leads to our alienation of it which can have negative effects on our mental health. One way to describe it is through the term nature deficit disorder, which is the concept that certain behavior disorders in children are linked to their lack of interaction with nature. Yet it applies to mental health on a larger scale.
Perhaps what it really comes down to when it comes to nature and mental health is our ability to use it for therapeutic purposes. One study found that nature walks help individuals manage depression. Animal assisted therapy has shown to be helpful for individuals living with schizophrenia. Gardening has been shown to help individuals living with dementia in terms of attention restoration.
There is of course much more to say on the way the two intersect but my point is, it is one avenue of mental health justice that does need more attention.