Dice the yellow onion, garlic, and jalapeno, and add into the slow cooker.
Add the beef shoulder into the slow cooker.
Cut the tomatoes into quarters then add into a food processor. Pulse until the tomatoes are crushed.
Add the tomato mixture into the slow cooker along with salt and pepper to taste.
Turn the slow cooker onto a high setting for 5 hours. You can then leave it on low until ready to serve, because the beef gets even more tender the longer it cooks.
Once the beef is tender, shred it apart with two forks and set aside.
Chimichurri:
To make the chimichurri, add all the ingredients into a small bowl and mix well, then set aside.
Quesadilla:
Pre-heat a grill pan on high heat.
Assemble the quesadilla by placing the shredded beef, chopped lettuce and chopped tomato over a tortilla, then closing it with another tortilla on top.
Place the quesadilla on the grill pan and sear for 1 minute on each side to get the grill marks and lightly toast the interior.
Cut the quesadilla into 4 quarters and enjoy with a serving of chimichurri sauce on the side.
Recipe by at https://seriousspice.com/shredded-beef-quesadillas-chimichurri/