01 - Season diced chicken breasts with salt and black pepper, coating evenly.
02 - Heat olive oil in a large, deep skillet over medium-high heat. Add seasoned chicken and cook until browned and cooked through, approximately 5 minutes. Transfer to a plate and set aside.
03 - In the same skillet, add chopped onion and red bell pepper. Sauté for 2-3 minutes until softened. Add minced garlic and cook for 30 seconds until fragrant.
04 - Stir in risoni pasta and dried Italian herbs; toast for 1 minute, stirring frequently to coat and lightly toast the grains.
05 - Pour in chicken broth and milk. Bring to a simmer, scraping up any browned bits from the bottom of the pan to incorporate flavor.
06 - Reduce heat to medium-low, cover, and simmer for 10-12 minutes, stirring occasionally, until risoni is tender and most liquid has been absorbed.
07 - Return cooked chicken to the skillet, add chopped spinach, and stir until spinach is wilted, about 1 minute.
08 - Remove from heat. Stir in mozzarella and Parmesan cheese until melted and creamy. Sprinkle with red pepper flakes if desired.
09 - Taste and adjust seasoning as needed. Serve hot, garnished with additional Parmesan cheese if desired.