Heat olive oil in a large skillet over medium-high heat and brown the sliced beef just until it develops some color, then transfer it to the slow cooker.

Add the sliced onion, bell peppers, and optional mushrooms to the slow cooker, spreading them evenly over the beef.

Sprinkle in the garlic powder, Italian seasoning, salt, and black pepper, then pour the beef broth around the ingredients.

Scatter the cubes of cream cheese over the top so they can melt slowly into the broth as it cooks.

Cover and cook on low for 5 to 6 hours or high for 3 to 4 hours, until the beef is tender and the vegetables are soft.

Stir the mixture well to fully blend the melted cream cheese into a smooth, creamy sauce, then add 1 1/2 cups of the shredded cheese and stir until melted.

Gently fold in the cheese tortellini during the last 20 to 30 minutes of cook time, cooking just until the pasta is plump and tender.

Sprinkle the remaining shredded cheese over the top, cover for a few minutes to melt, then garnish with fresh parsley and serve warm.