In a bowl, combine the potatoes, olive oil, salt and black pepper, toss to combine, and then transfer to a large baking sheet.
In the same bowl, combine the chicken breasts, olive oil, Italian seasoning, garlic powder and sea salt. Using your hands or tongs, toss the chicken in the spices until well coated. (If time permits, you could do this ahead of time and allow it to sit for up to 24 hours for extra flavour.)
Add chicken to the same baking sheet as the potatoes, leaving space in between each chicken breast so that they cook evenly. Transfer the baking sheet to the oven and allow to cook for 20 minutes.
While the chicken and potatoes are cooking, in a separate bowl, combine the tomatoes, onion, garlic, olive oil, balsamic vinegar, salt and half of the basil. Stir until well to combine and set aside.
After 20 minutes, remove the baking sheet from the oven, flip each chicken breast over and give the potatoes a good toss.
Top each chicken breast with shredded / sliced mozzarella and big spoonful of the tomato mixture until it has all been used. (You can also wait and top the chicken breasts with the cold tomato mixture once they are cooked, but I prefer it a bit warm.) Return the baking sheet to the oven and allow to cook for another 10 minutes until chicken is golden and cheese is bubbly.
Once cooked, remove the sheet pan from the oven and sprinkle each chicken breast with remaining fresh basil and a bit of parmesan to serve.
This dish can be served immediately, stored in the fridge for up to 5 days, or in the freezer in airtight containers for up to 3 months.