Dice the jalapeño pepper. Reserve the amount of seeds you’d like to add (remember, they are spicy!). Cut the half onion into a few chunks. Drain the can of tomatoes.
Place the jalapeño pepper and onion in a food processor. Pulse a few times to chop.
Add the cilantro, tomatoes, and green chilies to the food processor. Pulse several more times to achieve the desired consistency.
Stir in around 1 1/2 to 2 tablespoons apple cider vinegar and salt and pepper to taste. To add more spiciness, add another jalapeño, some red pepper flakes, or cayenne pepper.