1. Season the chicken breasts with salt, black pepper, and garlic powder. Heat the olive oil in a skillet over medium heat and cook the chicken for 5 to 6 minutes per side until golden and cooked through. Remove the chicken from the skillet and set aside.

2. In the same skillet, sauté the onion and garlic until softened. Add the crushed black peppercorns, oregano, parsley, and Worcestershire sauce. Gradually stir in the milk and then the cream cheese. Simmer until the sauce thickens slightly.

3. Cook the peeled and cubed potatoes in salted boiling water until fork-tender. Drain and mash with butter and milk to reach desired consistency.

4. Toss Brussels sprouts with olive oil, salt, and black pepper. Roast at 400°F for 18 to 22 minutes until caramelized.

5. Return the cooked chicken to the skillet with the creamy black pepper sauce, ensuring it is evenly coated. Spoon mashed potatoes into bowls, top with chicken, and add crispy Brussels sprouts.