Bearded dragon not fed properly

I’m in need of advice for my Beardie spike. He’s about 5-6 years old.

I asked a family member to look after him 3 years ago due to financial issues. I went to see him last week and saw that they hadn’t been looking after him properly and was told he’d only been fed cucumber for the last month. With the odd worm here and there.

His fat pads are sunken, and he’s weeing yellow (i’m Guessing it’s wee)

I’ve got him home again. We are in a better position now and I couldn’t leave him where he wasn’t being cared for. He’s not himself, spends most of his day laying flat including his head. We’ve deep cleaned his whole tank, been bathing him also.

Has anyone got advise on what I should feed him to get him back to health again?

Thankyou for reading and any advice anyone can offer.

Oh boy. Poor guy sounds like he's in rough shape. First thing I would do is get his lighting in order. Get the surface temps just right and order a good T5 UVB light for him if you don't already have one. http://www.lightyourreptiles.com/22-t-5-ho-fixture-high-output-with-arcadia-d3-12-ho-bulb/ Bring him outside for some natural sunlight when you can until the lighting is just right.

Once the infrastructure is in place for him to start absorbing nutrients properly, offer him a balanced diet of greens and veges. Give him water by dripping it on his nose to lick up and offer a salad with 2-3 items from this list each day http://www.beautifuldragons.com/Nutrition.html I would focus on things like chopped up green and yellow squash which will be hydrating for him. If he doesn't go for that on his own, try dripping some baby food on his nose to lick up. I've had good luck with green beans, squash, and sweet potato. If he responds to the water and at least the baby food, then he has a better chance at recovery so that's where I'd start.