Place the beef chuck roast pieces into the crock pot.
Add the sliced onion, minced garlic, diced tomatoes with green chilies (including the juice), ground cumin, chili powder, smoked paprika, salt, black pepper, and beef broth to the crock pot.
Stir gently to combine the ingredients around the beef.
Cover and cook on low for 6 hours, or until the beef is very tender and easily shredded with a fork.
Once cooked, remove the beef from the crock pot and shred it using two forks.
Return the shredded beef to the crock pot and stir to mix with the juices and seasonings.
Heat a large skillet over medium heat and add 1/2 tablespoon olive oil.
Place one flour tortilla in the skillet and sprinkle 1/4 cup shredded cheddar cheese and 1/4 cup shredded Monterey Jack cheese evenly over half of the tortilla.
Top the cheese with about 1/3 cup of the shredded beef and a sprinkle of chopped cilantro.
Fold the tortilla over to cover the filling and press gently with a spatula.
Cook for 2-3 minutes on each side or until the tortilla is golden brown and the cheese is melted.
Remove the quesadilla from the skillet and keep warm. Repeat the process with the remaining tortillas, cheese, beef, and cilantro, adding more olive oil to the skillet as needed.
Cut each quesadilla into wedges and serve warm with sour cream and salsa if desired.