Preheat oven to 190C/375F and put a large pan of water on to boil ready for the macaroni.
Starting with the garlic chicken, heat the oil in a large frying pan over a medium-high heat. When hot, add the chicken, salt, pepper, paprika and garlic salt. Cook for around 5 minutes until the chicken is almost cooked, then add the minced garlic and cook for a further 2-3 minutes. Transfer the chicken to a chopping board and slice into chunks.
By now the water should be boiling. Add in the macaroni and cook as per the pack instructions. Then drain in a colander.
Meanwhile, add the butter to the frying pan that you cooked the chicken in and heat on a medium heat until melted. Add the onion and cook for 5 minutes until softened.
Stir in the flour until it coats the onion, then a splash at a time, add the milk. Stir with a whisk between each addition of milk until all the milk is used and the sauce has no floury lumps.
Continue to stir whilst heating until the sauce starts to thicken. Add the salt and pepper, half the cheddar and all of the red Leicestershire. Stir until thickened, then turn off the heat.
Add the cooked macaroni and chicken to a large oven-proof dish, and pour over the sauce. Stir together, then sprinkle on the remaining cheddar and the mozzarella.
Place the panko, salt, pepper, paprika and oil in a bowl and stir together to lightly coat the panko in the oil, then sprinkle the panko on top of the macaroni.
Place in the oven and bake for 25-30 minutes until golden and bubbling.