Place the sliced onion in the bottom of the slow cooker crock. Nestle the chuck roast right on top. Sprinkle the garlic all over.
In a small bowl, whisk together the Worcestershire sauce, salt, pepper, dried thyme, basil, and minced garlic. Pour it over the roast.
Cook for 3-4 hours on high or 7-8 hours on low.
When the meat is fork tender, gently remove it from the crock pot and shred it. Return the meat to the crock pot and stir to evenly incorporate the meat, onions, and sauce.
Heat a large skillet or griddle (medium high heat or about 375 on the griddle). Place a tortilla shell down, cover with 1/2 cup shredded cheddar. Spread some of the beef over the cheese. Top with 2 ounces of provolone. Cook until the cheese is good and melty, place another tortilla on top, flip, and cook until the second side is toasty.
Remove to a cutting board.
Repeat with the other 3 quesadillas.
Slice them like pizzas and serve with shredded lettuce and sour cream.
Notes
I used green peppers and mushrooms in my quesadillas. You can add these to the slow cooker OR you can saute them quickly in a pan before adding to the quesadillas (I like the saute option, personally). [br][br]You'll have plenty of beef leftover. I am a huge fan of leftovers. You can use it for sandwiches, served over rice, to top a baked potato, make Philly cheese steak fries (why didn't I think of that until now?)-- the possibilities are pretty endless.