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.
Trim and core tomatoes. Dice and add to large glass bowl.
Juice limes. Chop cilantro. Add to tomatoes. Add salt, pepper, ground basil and cumin. Mix well.
Place in sterilized bottles and boil to seal for 10 minutes. Makes between 12 and 14 of the 250ml jars.