Add the garlic powder, Italian seasoning, cocoa powder, salt, and black pepper to a small bowl and stir to combine. Rub this mixture all over the surface of the chuck roast, pressing firmly to make sure it adheres. Set aside.

Heat two tablespoons of olive oil in a large pan (or in a Dutch oven if cooking this method) over medium heat. Once hot, add the seasoned chuck roast and brown on all sides, approximately 3-4 minutes per side.

Once browned, remove the roast from the pan and place in a slow cooker pot (or from the Dutch oven and transfer to a plate). Add the remaining tablespoon of oil and the Portobello mushrooms to the pan/Dutch oven and sauté, stirring occasionally, until the mushrooms develop some color and start to release their liquid, approximately 4-5 minutes.

Deglaze the pan/Dutch oven by adding the beef broth (use half of the beef broth if cooking in a slow cooker) and scraping up any brown bits on the bottom to incorporate them into the liquid. Stir in the tomato paste and add the bay leaves. If using a slow cooker, pour over the beef. If not, return the chuck roast to the Dutch oven and cover.

In the slow cooker, cook on high for 4-5 hours, or on low for 6-8 hours, or until the meat is fall-apart tender. Discard the bay leaves when cooked. Transfer the roast and mushrooms to a serving platter and cover to keep warm. Set aside.

In the Dutch oven, reduce heat to low and simmer for 3 to 3½ hours, or until the meat is fall-apart tender. Remove from heat and discard the bay leaves. Transfer the roast and mushrooms to a serving platter and cover to keep warm. Set aside.

Bring the liquid in pan/Dutch oven to a boil over medium-high heat, then reduce the temperature down to medium for several minutes or until the sauce thickens a bit.

To serve, spoon some of the pan sauce over the beef, along with some of the mushrooms. Garnish with fresh parsley, if desired, and pair with creamy mashed cauliflower or your choice of sides. Enjoy!