Adjust rack to top position and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Wash and dry all produce. Finely dice tomato. Pick basil leaves from stems; roughly chop leaves.

Pat chicken dry with paper towels. Season with salt, pepper, and half the Italian Seasoning (you’ll use the rest later). Heat a drizzle of oil in a medium pan over medium-high heat. Add chicken and cook until browned, 2-3 minutes per side. Transfer to a baking sheet. Top with half the mozzarella (save the rest for garnish). Bake until chicken is cooked through and cheese has melted, 9-11 minutes.

Once water is boiling, add spaghetti to pot. Cook until al dente, 9-11 minutes. Reserve 1/2 cup pasta cooking water, then drain. Reserve empty pot for use in step 5.

Heat a drizzle of olive oil in pan used for chicken over medium-high heat. Add tomato and remaining Italian Seasoning. Cook, stirring, until slightly softened, 1-2 minutes. Stir in vinegar and 1/4 tsp sugar (1/2 tsp for 4 servings). Simmer until mixture is slightly thickened, 1 minute. Remove from heat and stir in 1 TBSP plain butter (2 TBSP for 4) until melted. Stir in half the basil and season with salt and pepper.

Heat pot used for pasta over low heat. Stir in drained spaghetti, garlic herb butter, 2 TBSP reserved pasta cooking water (4 TBSP for 4 servings), and 1 TBSP plain butter. Stir in remaining basil and season generously with salt and pepper.

Slice chicken crosswise if desired. Divide spaghetti between plates and top with chicken. Spoon balsamic tomato over chicken. Sprinkle with remaining mozzarella and serve.