Preheat the oven to 375 degrees F (190 degrees C).
In a small bowl, combine the Ground Cinnamon (1/4 teaspoon), Chili Powder (1/4 teaspoon), Salt (1/4 teaspoon), and Ground Black Pepper (1/4 teaspoon).
Put the Boneless Pork Shoulder (2 pound) on a plate and rub the entire surface with the spice mixture.
In a cast-iron skillet over medium-high heat, warm the Olive Oil (3 tablespoon). Add the roast and brown on all sides, about 2 minutes per side. Transfer the roast back to the plate and set aside.
Add the White Onion (1) and Garlic (3 clove) to the skillet. Cook, stirring often until softened, about 4 minutes.
Return the roast to the skillet. Pour the juice of 3 Orange (3) over the roast and sprinkle it with the 3 Tbsp of orange zest and Dried Oregano (1 tablespoon).
Place the orange rinds around the roast. Cover and place the skillet in the oven to cook for 2 hours.
Remove from oven and let rest for 5 minutes. Cut into pieces and serve with freshly warmed flour tortillas.