Do you know the age of the dragon?
At certain stages in a dragon's life you have to real careful about fatty foods, they can cause serious health problems down the line.
Is it eating well or, is it a bit sketchy?
If the dragon is suffering from malnutrition, you have to go slowly so it can get it's metabolism going at first. Dubia Roaches, BSFL (black soldier fly larva) and, silkworms are great staple feeders to start with. If he/she is fed properly the weight will come in time.
Greens like turnip greens, mustard greens and, collard greens should be offered every day and, IF your new dragon (aka;boss aka;master) is over the age of 18 months, 80% of it's diet should be veggies and, 20% bugs. The opposite applies if it is under 18 months.
I hope this helps you a little and, if you have any other questions feel free to ask.....remember.... the only dumb question is one that is not asked