Preheat and prep: Heat oven to 375°F (190°C). Grease a medium casserole dish (about 2 to 2.5 quarts) with butter or a light coat of oil.
Sauté aromatics: Warm oil or butter in a skillet over medium heat.
Add onion and cook until soft, about 4 minutes. Stir in garlic and cook 30 seconds more, just until fragrant.
Soften the veggies: Add chopped vegetables to the skillet with a pinch of salt. Cook 4–6 minutes, stirring, until slightly tender.
They’ll finish in the oven, so don’t overdo it.
Mix the sauce: In a large bowl, whisk the condensed soup (or homemade white sauce) with milk or broth. Season with paprika, thyme, salt, and pepper. Fold in half the shredded cheese.
Combine the base: Add cooked rice, protein, and the sautéed vegetables to the bowl.
Stir gently until everything is coated and evenly mixed.
Assemble: Spoon the mixture into the prepared casserole dish. Smooth the top, then sprinkle with the remaining cheese.
Add crunch: Toss breadcrumbs or crushed crackers with a teaspoon of melted butter or oil. Scatter evenly over the cheese layer.
Bake: Cover loosely with foil and bake for 15 minutes.
Remove the foil and bake another 10–15 minutes, until the topping is golden and the casserole is bubbling at the edges.
Rest and garnish: Let it sit 5–10 minutes before serving so it sets slightly. Sprinkle with fresh parsley or green onions if you like.