Start a filling meal (6)
I believe the answer is:
Here is my best explanation:
'start' is the definition.
(launching is a kind of starting)
'a filling meal' is the subsidiary indication.
'filling' means one lot of letters goes inside another.
'meal' becomes 'lunch' (lunch is a kind of meal).
'a' going within 'lunch' is 'launch'.
(Other definitions for launch that I've seen before include "Start - motor-driven boat", "starter?", "Send on course, ship or book", "Set afloat or propel into action", "Embark", "Set on course, new ship or book", "Set in motion", "Propel on course, ship or rocket", "Power-driven boat" and "Boat; put in the water".)