Tube, first bit of pasta in dish (4)
I believe the answer is:
pipe
'tube' is the definition.
(pipes are tubular)
'first bit of pasta in dish' is the wordplay.
'first bit of pasta' becomes 'p' (1st letter of 'pasta').
'in' means one lot of letters goes inside another.
'dish' becomes 'pie' (I've seen this before).
'p' inserted inside 'pie' is 'PIPE'.
(Other definitions for pipe that I've seen before include "'Tube for water or gas, say (4)'" , "Duct; briar" , "Transmit through a tube" , "Utter shrilly; wine cask" , "Fluid or gas transporter" .)