Prepare the meat rub: Mix the paprika, chili powder, onion powder, garlic powder, and salt in a bowl.
Prick both sides of the meat in several places ( about 20-30 “hits”) using the tip of a sharp knife. Then pat dry the meat on both sides using a sheet of paper towel.
Rub the spice mixture over both sides of the meat. Wrap it tightly with stretch film or plastic wrap and let it marinate in the fridge for at least 4 hours or preferably overnight (up to 8 hours.)
On the day of cooking, remove the meat from the refrigerator and let it rest for 30 minutes while you prepare the rest of the ingredients.
Remove the stretch film. Sprinkle it with the flour on both sides, shaking off the excess.
Whisk together beef broth and tomato paste in a measuring cup until combined. Set it aside.
Place half of the sliced onions, pepper, and minced garlic at the bottom of the slow cooker. Place the meat with the fat side up on top of the mixture.
Add the remaining sliced onions, pepper, and minced garlic on top of the meat. Pour the mixture over the meat. Add the thyme and bay leaves to the liquid.
Cover and cook on low heat setting for 8-10 hours or until meat is fully cooked and shreds easily.
Transfer the now-cooked brisket onto a cutting board (or cookie sheet) and cover it with aluminum foil to keep it warm. Right before serving, shred the meat using two forks. When done, cover it with aluminum foil to keep it warm.