Combine paprika, oregano, cumin, salt, pepper, garlic powder, onion powder, turmeric, and cayenne pepper in a bowl; rub onto the non-fat side of pork belly. Cover with plastic wrap and refrigerate, at least 2 hours and up to overnight.
Preheat oven to 450 degrees F (230 degrees C). Line a rimmed baking sheet with parchment paper.
Remove plastic wrap from pork belly and place pork belly, fat-side up, on the prepared baking sheet. Make shallow cuts into the fat of the pork belly in a checkered pattern. Rub lemon juice into the fat.
Roast in the preheated oven until fat begins to brown, 30 to 40 minutes. Reduce oven heat to 350 degrees F (175 degrees C) and continue cooking until fat is crispy, about 1 hour more. Remove from oven and let rest 10 to 15 minutes before slicing.