Preheat large deep skillet on medium heat and swirl 1 tbsp oil to coat. Add chicken, ¼ tsp salt and pepper. Cook for 5 minutes, stirring once.
Move chicken to the side of the skillet and keep empty part over the burner. Add 1 tbsp oil, garlic and saute for 30 seconds, stirring frequently.
Add tomatoes, tomato paste, balsamic vinegar, oregano, ¼ tsp salt and a handful of basil. Cook this "tomato pile" for about 5 minutes, stirring occasionally.
Add zucchini, stir everything together, cover and cook on low-medium for 12 minutes.
Lay mozzarella slices on top, reduce heat to low, cover and simmer for 5 minutes.
Sprinkle more basil and ground black pepper on top. Serve hot, on its own or with spaghetti, Instant Pot brown rice or Instant Pot quinoa.
