Bring 2 1/2 litres (5 litres for 4 servings) salted water to a boil in a large pot over high heat. Add bucatini pasta and cook for 8-10 minutes or until al dente. Strain through a sieve then add back to pot and drizzle with olive oil.
Heat 2 tbsp. (4 tbsp. for 4 servings) oil in a large skillet over medium-high. Pat chicken breast dry using paper towel, and season with salt, pepper, and half of the italian seasoning. Add chicken to skillet and sear for 2 minutes on each side, or until golden and crispy.
Prepare Pesto Sauce
Reduce heat to medium-low and add garlic, and tomato paste. Stir into oil. Add 1 cup (2 cups for 4 servings) water, crushed tomatoes, pesto, red pepper flakes to taste, remaining italian seasoning, and balsamic vinegar. Stir. Let sauce simmer gently until chicken is cooked to an internal temperature of 165 F.
Meanwhile, wash basil. Roughly chop spinach. Julienne basil leaves.
When chicken is cooked, add spinach and basil to the skillet and stir until spinach is wilted and bright green.
Place chicken breast onto plates. Add pasta to the skillet and toss to coat in sauce. Divide onto plates next to the chicken. Sprinkle with parmesan cheese. Enjoy!