At 22 I had become strong and heavy built, but way too fat.

Most of my result back then have just been from newbie gains and eating too much (bad food even). Over the years I got weak and skinnyfat.

I have been hitting the gym and lost most of my fat last year, I'm at 15% and now I want to start focusing on regaining the lost muscle mass.

I want to hit the gym smart this time, any input as to which workout routine will regain muscle fast as it should come easier due to muscle memory?

TLDR: I was fat but buff at 22, now "lean" but weak at 30.