Place the cubed chicken in a large bowl and season with 1 tablespoon Italian seasoning and 1¼ teaspoons kosher salt. Toss to coat and set aside.
Heat 1 tablespoon extra virgin olive oil in a wide, ovenproof pot over medium heat. Add the chicken and cook, turning often, until browned on all sides and nearly cooked through, about 12 to 15 minutes. Transfer to a bowl.
Add the onion to the pot and sauté for 5 to 6 minutes until it softens. Add the garlic and sauté for 1 minute until fragrant.
Pour the mirin into the pot and scrape up anything stuck to the bottom. Bring to a boil and add the chicken. Stir to coat.
Simmer the sauce:
Pour the tomatoes into the pot and bring to a boil. Season with a pinch of salt, black pepper, and crushed red pepper. Reduce the heat to low and partially cover the pot. Simmer for 30 to 45 minutes or until the sauce reduces and thickens. Stir occasionally to prevent the sauce from sticking. Taste and adjust the seasonings to your preference.
You can add more mirin for a more pronounced sweetness.
Boil the pasta:
Bring a large pot of salted water to a boil. Cook the linguine according to package directions. Reserve ¼ cup of the pasta cooking water before draining.
Finish the pasta:
Turn on the broiler. Add the pasta cooking water to the pot of sauce and return it to a low boil. Add the cooked pasta and toss to coat for 1 to 2 minutes.
Cover the pasta with mozzarella cheese and place under the broiler for 3 to 4 minutes or until the cheese is bubbly and browned.