Young dragons often pay no interest in greens, preferring to eat live foods.
Most dragons make the transition naturally to eat more greens and less live food at the rough age of 18 months - 2 years. A good staple for greens in the UK is spring greens (sold in most supermarkets, Sainsburys sell a large bag for 99p!) watercress is a good staple as is rocket. Cucumber is best given as a treat as you know. Cress is another good staple option and is very inexpensive. We keep a constant supply in our beardie's viv of greens and cress, she never touches it, but we still supply it to her daily.
Young beardies need to be fed in my opinion 2 - 3 times daily with live foods of you're choice dusted appropriately, as many as they can eat in a space of 15 minutes or so. If you are going to feed crickets be sure to remove any uneaten ones at lights out as it has been suggested that crickets will infact have a nibble on your beardie as he/she sleeps
, I don't take any chances I remove any uneaten cricks.