Unroll roast, and trim fat. Spread 1 tablespoon Oregano Pesto into the folds of the roast. Reroll roast, and secure at 1-inch intervals with heavy string. Make several 1/2-inch-deep slits in surface of roast; stuff garlic slices into slits. Cut 3 additional 1/2-inch-deep slits in surface of roast; stuff 1 teaspoon pesto into each slit. Spread remaining pesto over surface of roast, and sprinkle with salt and pepper. Place roast on a broiler pan, and insert meat thermometer into thickest portion of roast; set aside.
Remove the white papery skin of garlic, making sure not to peel or separate the cloves. Wrap the garlic head in aluminum foil.
Bake roast and garlic at 325° for 45 minutes. Remove garlic from oven; set aside. Bake roast an additional 40 minutes or until thermometer registers 150° (medium-rare). Let roast stand 10 minutes before slicing. Separate garlic head into cloves, and serve with roast.