Prepare the ingredients by cutting the chicken into bite-size pieces, dicing the onion, mincing the garlic, and rinsing the rice under cold water until the water runs mostly clear. Drain the rice well.

Heat the olive oil and butter in a large, wide pot or deep skillet over medium-high heat. Add the chicken pieces in a single layer, season lightly with salt and pepper, and sear for 3–4 minutes, stirring once or twice, until lightly browned on the edges but not fully cooked through. Transfer the chicken to a plate and set aside.

Reduce the heat to medium. In the same pot, add the diced onion and a pinch of salt. Cook for 3–4 minutes, stirring occasionally, until softened and translucent. Add the minced garlic and cook for 30–60 seconds until fragrant, being careful not to let it brown.

Add the rinsed and drained rice to the pot with the onions and garlic. Stir for 1–2 minutes to coat the rice in the fat and lightly toast it, which helps the grains stay separate and flavorful.

Stir in the dried thyme, dried oregano, sweet paprika, and bay leaf. Pour in the chicken broth and heavy cream, scraping the bottom of the pot with a wooden spoon to release any browned bits. Add 1 teaspoon of salt and the black pepper, then stir to combine.

Return the browned chicken and any accumulated juices to the pot. Add the mixed vegetables and stir everything together so the chicken, rice, and vegetables are evenly distributed in the liquid.

Bring the mixture just to a gentle boil over medium-high heat. As soon as it starts bubbling, reduce the heat to low, cover the pot with a tight-fitting lid, and let it simmer gently for 15–18 minutes, without lifting the lid too often, until the rice is tender and most of the liquid is absorbed.

After 15 minutes, quickly lift the lid and check the rice. If it is still a bit firm and there is very little liquid left, add a splash of broth or water, cover again, and cook for another 3–5 minutes. The final texture should be soft and creamy, similar to a loose risotto, not dry.

When the rice is tender and the chicken is cooked through, remove the pot from the heat. Remove the bay leaf. Stir in the cream cheese or mascarpone, if using, until melted and fully incorporated. Add the lemon juice and adjust the seasoning with more salt and pepper to taste.

If using, stir in the grated Parmesan cheese or sprinkle it over each portion when serving. Let the dish sit, covered, for 3–5 minutes to thicken slightly, then garnish with chopped fresh parsley or chives and serve warm in bowls.