Cut in half a large white onion, remove skin and chop into large chunks.
Add to a food processor. Add cilantro and jalapeno, if you are using, to the food processor and use the chop setting on your processor.
Run the food processor until the cilantro, onion, and jalapeno are finely chopped.
If you don't want to use the food processor, that is just fine! Finely dice the onion, cilantro, and jalapeno on your own.
Add cilantro and onion mixture to a large mason jar, I use a quart size (32 ounces).
Pour the tomato sauce until it reaches about an inch from the top.
Add seasonings, salt, cumin, and chili powder.
Screw on the mason jar lid and shake until well combined. Use immediately or let it sit in the refrigerator until ready to use.
Enjoy!