Preheat and prep. Heat your oven to 400°F (200°C).
Lightly grease a baking dish or line it with parchment for easy cleanup.
Steam or microwave the broccoli. Cook the chopped broccoli just until tender-crisp—about 2–3 minutes in the microwave or 3–4 minutes steamed. Pat dry with paper towels to remove excess moisture.
Make the filling. In a bowl, mix broccoli, cheddar, cream cheese, Parmesan, mayonnaise, garlic, onion powder, smoked paprika, Italian seasoning, 1/2 tsp salt, and pepper. Stir until smooth and well combined.
Butterfly the chicken. Place a chicken breast on a cutting board.
With your hand flat on top, slice horizontally to create a pocket, stopping about 1/2 inch from the other side. Repeat with the remaining breasts. Season the outside of each breast with a pinch of salt and pepper.
Stuff the chicken. Spoon the broccoli-cheese mixture into each pocket, dividing it evenly.
Don’t overfill; you may have a tablespoon or two left depending on breast size. Secure the opening with toothpicks.
Sear for color (optional but recommended). Heat olive oil in a large oven-safe skillet over medium-high. Sear chicken 2–3 minutes per side until lightly browned.
If you don’t have an oven-safe skillet, transfer seared chicken to your prepared baking dish.
Bake. Place in the oven and bake 18–22 minutes, or until the thickest part reaches 165°F (74°C). Cooking time can vary based on breast size and how much you seared.
Rest and serve. Let the chicken rest 5 minutes. Remove toothpicks and slice.
Spoon any melted cheesy goodness from the pan over the top. Serve with a simple salad, roasted cauliflower, or sautéed greens.