While the rice and chicken cook, in a large, deep skillet or dutch oven over medium high heat, melt butter.
When butter is melted, add onion and garlic. Saute until softened, 5-7 minutes. Once softened, add crushed tomatoes, diced tomatoes and tomato paste. Stir well and simmer 3-4 minutes.
Add remaining seasonings, 3/4 of the chopped basil, and the balsamic vinegar. Stir well. Reduce heat to low and simmer for 10 minutes.
Add rice, shredded chicken, spinach and half of the mozzarella. Stir well and remove from heat.