Place the orange zest, lemon zest, rosemary, parsley, fennel seeds, garlic, olive oil, chili flakes, salt, and pepper into a food processor and pulse to make a paste.
Butterfly the pork loin by cutting a slit all along the side, this way it opens to look like a book. Lather half of the spread on the inside of the pork then roll it and roughly tie it with the butcher string. Place the other half of the spread on the outside of the roast. (The roast can be prepared and marinated for up to two days or frozen for up to three months).
Wash, peel and cut all the vegetables into about the same size. Place at the bottom of the roasting pan and drizzle with olive oil, season with salt and pepper. Toss to coat.
Place the roast on top of the vegetables and cover with aluminum foil. Cook slowly for up to one-and-a-half hours.
Verify the roast using a digital thermometer to ensure that the internal cooking temperature is 145 degrees Fahrenheit. Then remove from the oven and allow it to rest 10-15 minutes before cutting. Remove the butcher string and slice it so that the inside can be showcased. Serve alongside all the vegetables that you roasted.
You can always use the pan drippings as a sauce or produce a gravy using the drippings.