Prep your veggies. Peel the garlic. Peel and quarter the onion. Remove the seeds and ribs from the jalapeño. (Save the seeds for a hot salsa.) If tomatoes are large, quarter them; otherwise, leave them whole.
Place the green tomatoes, garlic, onion, and jalapeño on a baking sheet. Broil on high for 4 to 5 minutes until just beginning to blacken.
Flip and rotate the veggies and broil another 4 to 5 minutes.
Transfer everything to a food processor or blender, except use only 1/2 of the jalapeño.
Add the cilantro, kosher salt, and lime juice. Pulse until the desired consistency is reached.
Taste, and if you’d like it hotter, add the other 1/2 of the jalapeño and/or some seeds. You may want to refrigerate until serving, since the salsa will be warm from the roasting, or leave it at room temperature until serving. Stores up to 1 week refrigerated.