Preheat your oven to the broil setting. Cut all of the tomatoes in half and roughly slice the onion. Place the tomatoes cut side up on a baking sheet along with the onion, garlic, and jalapeño. Broil the veggies until cooked through and slightly charred, about 15-20 minutes.
Place the roasted veggies into a blender or food processor and pulse until combined and just slightly chunky, yet fairly smooth. Add in the salt, cilantro and lime and pulse until the cilantro is incorporated.
Taste and add more salt, cilantro or lime to your preferences.
Notes
I've made this salsa without roasting the veggies and it works great as well. So if you're in a time crunch, just add everything raw into a blender and puree until your desired consistency!