Preheat the oven to 375°F (190°C). Position a rack in the middle so the rice cooks evenly and the cheese can melt without browning too fast.
Season the chicken: Pat chicken dry with paper towels so the seasoning sticks. Sprinkle both sides with salt, pepper, garlic powder, Italian seasoning, and paprika. Let it sit 5 minutes while you prep the rice mixture (this helps the seasoning absorb).
Prep the baking dish: Lightly coat a 9x13-inch baking dish with a thin layer of olive oil (or spray). This prevents sticking and helps the rice release cleanly when serving.
Build the flavor base: If you want the best flavor, warm olive oil in a small skillet over medium heat and sauté the onion for 3 to 4 minutes until soft, then add garlic for 30 seconds. If you are short on time, you can skip sautéing and add onion and garlic directly to the dish (the bake still works, just slightly less aromatic).
Add rice to the dish: Spread the uncooked long-grain rice evenly across the bottom of the baking dish. If you sautéed onion and garlic, scrape them in now. Spreading rice evenly is important so it cooks at the same rate and does not clump.
Add tomatoes and seasonings: Drain diced tomatoes well, then stir them into the rice. Add oregano and basil. Draining is key because extra tomato liquid can lead to overly soft or watery rice.
Pour in broth and level the mixture: Pour chicken broth over the rice mixture and stir once to combine. Use the back of a spoon to level the rice so it is in an even layer. An even layer helps the rice absorb liquid uniformly.
Place chicken on top: Lay the seasoned chicken on top of the rice in a single layer. Do not push it down into the rice. Keeping it on top prevents the chicken from getting rubbery and lets the rice cook underneath in the broth.
Cover tightly and bake: Cover the dish tightly with foil. Bake for 35 to 40 minutes. Tight coverage traps steam, which is what cooks the rice properly. If foil is loose, the rice may turn dry or undercooked.
Check doneness correctly: Remove foil carefully (watch for steam). Check that the rice has absorbed most of the broth and is tender. Check chicken temperature with an instant-read thermometer in the thickest part. Chicken should be 165°F (74°C). If rice is still firm, add 1/4 cup broth, re-cover tightly, and bake 8 to 12 minutes more.
Add the creamy finish: Once rice is tender and chicken is cooked, stir heavy cream into the rice around the chicken (do not aggressively stir the chicken). Sprinkle Parmesan and mozzarella evenly over the top. The cream makes the dish taste richer and more casserole-like without making it heavy.
Melt and lightly brown: Return to the oven uncovered for 5 to 10 minutes until cheese is melted and lightly golden. If you want more color, broil for 1 to 2 minutes, watching closely.
Rest before serving: Let the dish rest 5 minutes. This helps the rice set up and makes servings cleaner. Garnish with chopped parsley and serve warm.