。
I do my best work when I'm under pressure.
Literal
I [topic-は] be-pushed-cornered-[passive-れる]-[when-と] most work [object-を] do.
追い込まれる is the passive of 追い込む ('corner, push into a corner'), meaning 'be cornered, be under pressure, be driven.' ~と conditional for habitual/inevitable results. 一番 ('most, the most') as an adverbial intensifier. A self-description of one's work style.