To start with, peel the garlic. Once it is done, you have to peel and quarter the onion. From the jalapeno, remove the seeds and ribs. These seeds can be used later for making the salsa more spicier. If your green tomatoes are large in size, quarter them. In the case of smaller sized ones, leave them whole.
Keep the green tomatoes, onion, garlic and jalapeno on the baking sheet. For around 4 to 5 minutes, broil on high till it starts to blacken. Flip and rotate all the vegetables. Now you have to broil again for 4 to 5 minutes.
Move all the above ingredients, except the entire jalapeno to a food processor or blender. Please note that you have to use only ½ of the jalapeno here. Now add the cilantro, lime juice and kosher salt. Press the pulse button on your food processor till it reaches the desired consistency.
Now, it's time to taste the green tomato salsa. If you prefer to have it hotter, then add the remaining half of the jalapeno. You can also add some seeds.
Now, your salsa will be warm due to the roasting. Before serving, you may want to refrigerate the green tomato salsa or leave it at room temperature. If refrigerated, you can use the dish for upto 1 week.