Turn oven on to broil (high). Move the oven rack you will be using up to the 2nd position from the top. This will ensure that we get a nice char, which is essential to the salsa's flavor.
Line a rimmed baking sheet with parchment or foil. Do NOT oil the pan, this will cause a lot of smoke.
Slice tomatoes, onion, jalapeño into even 1-inch slices and arrange in a single layer on a large baking sheet. It is important to slice all the ingredients evenly so that it all chars evenly and cooks at the same speed.
Smash the cloves of garlic and add to the baking sheet.
Once the oven is ready, place the baking sheet on your top rack. Broil for 10-20 minutes. Broil time may vary depending on your oven, so it is essential that you watch for the right amount of char.
Once the veggies have reached the desired char level, take the baking sheet out of the oven and let cool for 5-10 min. While this cools, we'll add our remaining ingredients.
Squeeze both limes over the cooling veggies, then evenly sprinkle on all the seasoning. Gently mix or toss everything together on the pan.
Once the veggies and warm, transfer everything into a blender or food processor. Include any liquid or juice left in the pan. Pulse it a few times and then continue until it reaches the desired texture (chunky, smooth, or somewhere in between).
Pour into a mason jar or similar Refrigerate for 2 hours or overnight for best taste.