Preheat the oven to high broil.
Clean and pat dry chicken breast. If chicken breasts are not even in size, place chicken in a plastic zip bag, use a blunt object such as a rolling pin and pound chicken into about ¼ - ½ inch thickness.
Add chicken breast to bowl, toss in olive oil, salt, black pepper, garlic powder, Italian seasoning, and smoked paprika.
In a cast iron skillet on medium-high heat, add in avocado oil. Once oil is brought up to temperature add in chicken breast. Cook chicken for about 4-5 minutes each side or until fully cooked.
Remove chicken from skillet and set aside. Add in butter. Once butter is melted, add in diced onions. Cook onions for about 2-3 minutes, then, add in minced garlic and cook for 1 minute.
Add in diced tomatoes and chicken broth and bring to a simmer. Season with salt & black pepper to taste and add in white sugar to cut the acidity of the tomatoes. Scrape up bits from cooking chicken and simmer for about 5 minutes or until tomatoes blister. Then, add in spinach, mix in, and cook for about 2 minutes or until spinach is wilted.
Add chicken to the skillet. Top chicken with shredded mozzarella and broil for 2-3 minutes or until cheese is melted and slightly browned.
