In a small skillet, heat the olive oil and chili flakes over low heat for 1 minute. Turn off the heat and add the oregano, garlic and lemon zest. Pour mixture out of the pan and into a bowl. Allow to cool.
For the lamb skewers:
Slice lamb loin lengthwise (as if filleting) into 2 pieces about 1/2-inch thick. Using a mallet or the heel of your palm, lightly pound meat to about 1/4-inch thickness then cut each in half lengthwise. Place meat in a non-metallic dish and pour reserved oregano marinade over the meat. Turn several times to coat, cover, and refrigerate at least 1 hour or overnight.
When ready to cook, prepare grill or preheat broiler.
Remove lamb from marinade and discard marinade. Spread about 1 tablespoon garlic paste on each of the lamb pieces. Season with salt and pepper. Roll meat lengthwise end to end and place on skewers. Brush with olive oil. Grill or broil to desired doneness, 10 to 15 minutes for medium-rare meat, depending on heat of grill. Turn meat occasionally to ensure even cooking.
Preheat the oven to 350 degrees F.
Peel the outermost layers of skin off the heads of garlic. Cut off the top 1/3 of the heads to open the cloves. Put the heads, cut sides up, in a small baking dish and pour the olive oil over them. Season with salt and pepper. Cover tightly, place in the oven, and roast until about 3/4 cooked, about 45 minutes. Uncover and return to the oven until the cloves begin to pop out of their skins and brown, about 15 minutes. Let cool.
When garlic is cool enough to handle easily, squeeze the roasted garlic into a small bowl. Press against the skins very well to get out all the sweet roasted garlic you can. Add the oil from the baking dish and mix well until a paste forms. Store, tightly covered, in the refrigerator, for up to 1 week.
If buying fresh lamb, make a double batch and freeze half on the skewers. Convenience and compromise are cousins: Lamb is a meat that freezes very well. Make sure to transfer meat from the freezer to the refrigerator the day before you plan to serve it to ensure even thawing. To toast the red pepper flakes: Put red pepper flakes in a skillet and heat over medium heat just until flakes begin to brown. Immediately remove from heat and pour onto a cool dish to prevent burning.