Green peas are rich in iron and contain compounds that improve nail color.
Literal
Green-peas [topic-は] iron [subj-が] abundant [and-で] nails [gen-の] color [subj-が] good-become compound [subj-が] contained-[progressive-ている].
鉄分が豊富 'rich in iron' (鉄分 'iron content' + 豊富 'abundant') is a standard nutritional claim. 成分 'compound/ingredient' is nominally modified by the relative clause 爪の色がよくなる 'that makes nail color better.' The double-が structure puts 鉄分が and 成分が in parallel subject roles — a common feature of informational prose.