He said sesame and lettuce in buns are burger amateur's toppings (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A <nd> L <ettuce> I <n> B <uns> A <re> B <urger> A <mateur>; “toppings” means first letters only; the reference is to Open sesame , the magical phrase spoken by Ali Baba in Ali Baba and the Forty Thieves