Pat the beef chuck roast dry with paper towels and season generously with salt and freshly ground black pepper on all sides.
Heat the olive oil in a large skillet over medium-high heat until shimmering.
Sear the roast in the hot oil until browned on all sides, about 4 minutes per side. Transfer the roast to the slow cooker.
In the same skillet, add the chopped onion, carrots, and celery. Cook, stirring occasionally, until the vegetables are softened, about 5 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Transfer the cooked vegetables and garlic to the slow cooker, spreading them evenly around the roast.
Add the crushed tomatoes, tomato paste, and beef broth to the slow cooker. Stir gently to combine with the vegetables around the roast.
Sprinkle the dried oregano, dried basil, dried thyme, and red pepper flakes over the top. Add the bay leaf.
Cover the slow cooker and cook on low for 8 hours, or until the beef is very tender and easily shredded with a fork.
Remove the roast from the slow cooker and place it on a cutting board. Discard the bay leaf.
Use two forks to shred the beef into bite-sized pieces.
Return the shredded beef to the slow cooker and stir to combine with the sauce.
Taste the ragu and adjust seasoning with salt and freshly ground black pepper as needed.
Serve the pot roast ragu hot over cooked pasta, garnished with chopped fresh parsley.