Prep the oven and dish: Heat oven to 375°F (190°C). Grease a 9x13-inch baking dish with a little butter or oil.
Soften aromatics (optional but tasty): If using fresh onion and garlic, sauté them in a small pan with oil over medium heat until softened and fragrant, 3–4 minutes. Let cool slightly.
Combine the base: In a large bowl, whisk together condensed soup, broth, and milk until smooth.
Stir in salt, pepper, parsley, and paprika.
Add rice and veggies: Mix in the uncooked rice and your vegetables. If using frozen vegetables, no need to thaw. Fold in the cooked chicken.
Adjust creaminess: If you like it richer, stir in sour cream and/or half the shredded cheese.
Taste the sauce and adjust seasoning.
Assemble: Pour the mixture into the prepared baking dish. Spread evenly. If using cheese, sprinkle the remaining cheese on top.
Add topping (optional): Mix breadcrumbs or crushed crackers with melted butter and scatter over the casserole.
Bake covered: Cover tightly with foil and bake for 35–40 minutes.
This traps steam so the rice cooks evenly.
Finish uncovered: Remove foil and bake 10–15 more minutes, until the top is lightly golden and the rice is tender. If the edges look dry, splash in 1/4 cup hot water and return to the oven for 5 minutes.
Rest and serve: Let the casserole rest for 10 minutes. This helps the sauce set.
Garnish with a little extra parsley if you like.