Peel and cut onion into chunks. Cut jalapeno in half lengthwise. Place on foil lined tray and drizzle with oil. Cut top off garlic and wrap in tin foil with a few drops of water and oil on top. Roast onion, jalapeno, and garlic in a 375 degree F oven for 45 minutes. Let them cool. Once cool, chop up roasted onion and jalapeno. Place in large glass bowl. Squeeze garlic out of skins. Chop up any large chunks. Add to onions and peppers.