Preheat your oven to 400°F. While the oven heats, prepare your bell peppers by carefully cutting them in half lengthwise and removing all seeds and white membranes inside. Arrange the pepper halves cut-side up in a 9x13 inch baking dish, season lightly with salt and pepper, and set aside. This prep work ensures your peppers are ready to fill while you work on the filling mixture.

Heat the olive oil in a large skillet over medium heat and add the diced onions. Cook for about 5-7 minutes, stirring occasionally, until the onions become soft and translucent. Add the shredded chicken and cook for another 2-3 minutes, breaking it up as it heats through. This technique of softening the onions first allows them to release their natural sweetness, which creates a better flavor foundation than adding them raw.

Add the rice directly to the skillet with the cooked chicken and onions. Pour in the 2.5 cups of marinara sauce and stir everything together thoroughly to combine. Add the salt, pepper, chili powder, onion powder, and garlic powder, mixing well to distribute the seasonings evenly. The sauce will partially cook the rice and keep everything moist during baking.

Cook the rice mixture in the skillet over medium heat for about 5 minutes, stirring occasionally, to begin softening the rice and melding the flavors. Then stir in 1/2 cup of the cheese until fully incorporated. This helps bind the mixture and adds a creamy texture. Remove from heat and set aside.

Pour the 1 cup of marinara sauce into the bottom of the baking dish with the prepared peppers, spreading it evenly. This creates a flavorful base layer. Divide the chicken and rice filling from Step 4 evenly among the pepper halves, mounding it slightly. Top each filled pepper with the remaining 2 cups of cheese, distributing it generously across all peppers. Cover the entire dish tightly with aluminum foil.

Bake the covered dish at 400°F for 15 minutes. Remove the foil carefully and return to the oven for another 10 minutes, allowing the cheese to melt completely and develop a light golden color on top. I like to keep the peppers covered for most of the baking time so they stay tender without drying out, then uncover them at the end to let the cheese finish melting and get slightly golden.

Remove the baking dish from the oven and let it cool for 2-3 minutes. Top the peppers with fresh chopped parsley just before serving for a fresh, bright finish and a pop of color.