What is a memorable performance to you? Hattricks vs Real Madrid? Messi-esque playmaking on a No. 9 position with a gazzilion assists? Solo goals en masse? As such performances like his one vs Madrid for Dortmund don't happen on a yearly base, it's not surprising that there's a lack of examples to fit your criterias. This forum has declared all great strikers as overrated at least once, Suarez, Lewandowski, Kane, Griezmann, Higuain, Cavani etc and it's always after a lost big game and ESPECIALLY when said big game was against Madrid. It's like No. 9s are generally wank.
Not at all, those are extremes.
To point out some recent CL performances in recent history:
Mandzukic vs Real, Dybala vs Barca, Salah vs City, Mbappe vs City, Griezmann vs Barca, Higuain vs Monaco.
Edit: Oh and how could I forget Dzeko vs Barca
Not legendary performances/goals by any means, but very solid forward performances that influenced the CL ties.
Haven't seen Lewandowski be decisive like the examples mentioned above in big CL ties while with Bayern.
Still think he's been quite underwhelming for a player of his caliber. Reading around seems a lot of Bayern fans feel the same about him and Thiago as well.