Heat a large skillet over medium-high heat and add the oil.
Slice or chop the onion; add to hot skillet and cook until tender and caramelizing.
Add smashed garlic cloves to the onions and sauté 3-5 minutes until they soften and become fragrant. Season with the herbs and spices (paprika through thyme), then remove from the heat.
Season the roast with salt and pepper. Place it in a slow cooker (fat side up) and spread the onion mixture over top.
In a medium bowl, whisk together the ketchup, chili sauce, brown sugar, beef broth, and mustard; pour over the roast and onions.
Cover and cook on low for 6-8 hours or until meat can be easily shredded with a fork.
Meanwhile, dice tomato and slice bell pepper.
Once cooked through, shred beef and add to tortillas; add topping ingredients as desired.
Serve with grapes on the side.