There’s really nothing easier. 24 hours in a sous-vide bath set to 55C. I usually don’t marinate or season the meat beforehand unless I’m making Chinese roast pork, but if you want to add flavor when you cook, do it with a light hand. (Especially limit the amount of garlic, since a little goes a long way with sous vide.)
Once pork belly is cooked sous-vide, you can do almost anything with it. Chop it or shred it and douse it with your favorite sauce.
If I want to make carnitas out the pork belly, I set the heat a bit higher in the sous-vide (65C). When it’s finished, I fry the outside to crisp the fat and caramelize it. Then I shred the meat and serve with salsa. (You can also broil the meat after you take it out of the bath, but be careful not to overdo it or you’ll lose the lovely moist texture from cooking sous-vide.)