Heat the oven: Preheat to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Prep the broccoli: If using fresh, blanch in boiling salted water for 1 minute, then drain well. This keeps color bright and texture crisp-tender.
If using frozen, thaw and pat dry to avoid excess moisture.
Make the sauce: In a bowl, whisk together yogurt (or sour cream), mayonnaise, Dijon, garlic powder, onion powder, paprika, 1 teaspoon salt, and black pepper until smooth.
Season the chicken: Pat chicken dry. Cut large breasts in half lengthwise for even cooking. Rub with olive oil or melted butter and a pinch of salt and pepper.
Assemble the base: Scatter broccoli in the baking dish.
Nestle chicken pieces on top, leaving a little space between them.
Smother with sauce: Spoon the creamy mixture evenly over the chicken and broccoli. Don’t worry about perfection—just cover most surfaces so everything stays moist.
Add cheese: Sprinkle cheddar and Parmesan over the top. For a crunchy finish, mix panko with 1 tablespoon melted butter and scatter over the cheese.
Bake: Bake uncovered for 25–30 minutes if using tenders or thin-sliced breasts, or 30–35 minutes for thicker pieces.
The chicken is done when it reaches 165°F in the thickest part and the top is bubbling and lightly golden.
Rest and garnish: Let the bake sit for 5 minutes. Sprinkle with parsley or chives. A quick squeeze of lemon over servings brightens everything.
Serve: Spoon over rice, quinoa, or mashed potatoes, or pair with crusty bread for scooping up the sauce.