In a small bowl, mix together the cinnamon, cumin, cayenne, and salt, to taste. Rub the mixture all over the outside of the pork. In a large saute pan, heat the oil over medium-high heat and brown the pork roast on all sides, just until golden. Remove the pork to a sheet tray, fat side up.
Meanwhile, make the herb crust: In a food processor, combine the onions, garlic, ginger, cilantro, and lime zest. In the same saute pan in which the pork was browned, add the olive oil and the onion mixture and cook until softened. Stir in the bread crumbs and cook another 1 to 2 minutes. Season with salt, to taste. Spread the mustard on top of the fatty layer of pork and then press the herb crust into it. Bake until the internal temperature reaches 160 degrees F on an instant-read thermometer, about 30 minutes. Remove to a cutting board and allow to rest, covered for 5 to 10 minutes. Slice the roast, arrange on a serving platter and serve.