The simple 1. ... Nxb5 looks sufficient, but does not give black enough to win, thanks to the queenside pawn weakness induced by the WN's outpost.

1. ..b6 2. Rc4 Ne2+ 3. Kh2 Nxg3 4. Kxg3 and now ... Bd3 cements black's advantage. Now black can think of advancing those queenside pawns and squeezing W pieces on the queenside.

I don't have the time for a full study of this, but the only move that jumps out at me is 1....b6 attacking the precarious state of white's rook at c5. There are no good squares for the rook on the c-file that aren't attacked by the knight directly or indirectly by the fork from e2, and the squares on the 5th rank are no good either because Re5 would just block the bishop's coverage of the knight on c7. Best is probably 2.Rc4, but then white has 2....Bd3. Complicated, but I think black will come out ahead materially when all the dust settles, just not sure of all of the variations.