Preheat your oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish.
Pat the chicken dry.
Toss with olive oil, 1/2 teaspoon salt, black pepper, garlic powder, onion powder, and smoked paprika if using. Spread evenly in the baking dish.
Bake the chicken for 12–15 minutes, just until it turns opaque on the outside. It will finish cooking later.
Remove from the oven but keep the oven on.
While the chicken bakes, make the ranch sauce. In a bowl, whisk mayonnaise, sour cream, heavy cream, lemon juice, dill, parsley, chives, garlic, onion powder, remaining salt, and pepper. Adjust thickness with a splash more cream if needed.
Taste and season.
Add the diced avocados and chopped chives/green onions to the par-cooked chicken. Pour the ranch sauce over the top and gently fold to coat everything evenly.
Sprinkle mozzarella and cheddar over the mixture in an even layer.
Return to the oven and bake for 10–12 minutes, until the cheese is melted and bubbly and the chicken reaches an internal temp of 165°F (74°C).
Broil for 1–2 minutes if you want extra browning on the cheese. Watch closely to avoid burning.
Let the bake rest for 5 minutes.
Garnish with extra chives or green onions before serving.