In a large skillet over medium-high heat, briefly sear the thinly sliced beef with the sliced onions and green pepper for about 3-5 minutes, just until the edges start to brown. Drain any excess liquid, then transfer the beef and vegetables to the basin of a 6-quart slow cooker.

In a medium bowl, whisk together the beef broth, cream of mushroom soup, Worcestershire sauce, garlic powder, salt, and pepper until smooth. Pour this mixture over the beef and vegetables in the slow cooker.

Cover the slow cooker and cook on LOW for 3.5 hours or on HIGH for 2 hours. The mixture should be hot and the beef tender.

Stir in the cubed cream cheese until it has melted and incorporated smoothly into the sauce. Then, gently stir in the uncooked frozen cheese tortellini.

Cover the slow cooker again and continue cooking on LOW for another 30-40 minutes, or until the tortellini are tender and cooked through according to package directions. Do not stir during this final stage to avoid breaking the pasta.

Once the tortellini is cooked, turn off the heat. Gently fold in the shredded mozzarella and the small pieces of provolone cheese. Let it sit, covered, for 5-10 minutes, allowing the cheese to completely melt and become gooey.

Serve immediately, optionally garnished with fresh parsley or a dash of onion powder.