Preheat sauté pan on medium high heat.
Pat dry and season chuck roast with kosher salt and freshly ground black pepper.
Add avocado oil to hot pan and sear chuck roast, 3 minutes per side.
Place potatoes, baby carrots, onions and fresh thyme sprigs in slow cooker, put seared chuck roast on top of vegetables.
Deglaze pan with beef stock. Scrape bits off the bottom of pan. Add crushed tomatoes and tomato paste. Whisk to break up tomato paste. Simmer for 2 minutes then pour over roast and vegetables.
Set slow cooker on high setting for 6-8 hours, or low setting for 12-16 hours. Enjoy!