This exercise is funny for Spaniards. Popcorns were introduced in Spain as corn flowers, then a trade mark Palomitas (little doves) became so popular, that currently popcorn is only known as palomitas in Spain.
the pronunciation of the lambda sounds so much like an "n"
It may take some time to train your brain to hear it, but it is an "L" sound.
I remember when I first started speaking Spanish with native speakers I had trouble distinguishing the words "lo" and "no" (which have very different meanings). But after a few months, I wondered how I ever got them confused. They no longer sound at all alike to me.
In Spanish the L sound is harder than the English one, and that may be why I confused it with N. It may be something similar for you in Greek. English teaches us that if it's not a liquid sound, it can't be an L, so your brain tries to come up with a different sound.
But don't worry, with practice you'll start catching on to the pronunciation.
Try saying "lu" but make your tongue tense. Practicing that will help.