Preheat the oven to 375°, if roasting the pork right away. Oil a medium roasting pan. Coarsely chop the garlic on a board. Add the rosemary, salt, and fennel seeds, and chop fairly fine, crushing the mixture with the flat side of a chef’s knife. Scrape the mixture into a small bowl and stir in the black and red peppers.
If the roast is not already tied, tie it every two inches with kitchen twine to maintain shape. With a paring knife, poke about 10 to 12 small holes all over the pork and insert a bit of the rosemary-garlic mixture into each. Rub the remaining mixture over the pork. Place it in the prepared roasting pan. If not roasting right away, loosely cover and refrigerate for 3 to 4 hours.
Before roasting, drizzle pork with the olive oil. Roast 50 to 60 minutes, basting a couple times with the pan juices, until an instantread meat thermometer inserted into the center registers 135° to 140°. Check after 40 minutes to prevent overcooking. Tent loosely with foil and let stand at least 10 minutes before carving and serving with the roast vegetables and pan juices.