Hollow out both halves of the fresh loaf by removing the crumb. Finely chop the chicken fillet, then fry it over medium-high heat for 5-7 minutes, stirring occasionally, until cooked through (internal temperature 74°C / 165°F). Place the cooked chicken on the top half of the hollowed loaf.
In a frying pan over medium heat, combine the tomato paste with 150 ml of water and salt, then add the basil. Simmer for 2-3 minutes until the sauce is warm.
Dip both halves of the loaf in the tomato sauce for about 2 minutes, coating them well.
Finely chop the onion and grate the cheese. Spread the onion and cheese on the bottom half of the loaf, pour 3-4 tbsp of aioli sauce, and sprinkle with parsley and dill. Close the sandwich by placing the top half (with chicken) on the bottom half, then microwave on high for 2-3 minutes until the cheese melts and the loaf is heated through.