Reheating chicken in a pasta bake-help please!

[Malkuth]

I want to use leftover roast chicken in a pasta and tomato sauce bake but am unsure of the safest route to take.

1. Do I cook pasta, heat sauce with chicken in and then top with cheese and bung under the grill?
2. Or do I cook pasta, put cold sauce and chicken in, top with cheese and put in oven for 20 mins?
3. Or do I microwave the chicken to reheat, put with hot pasta and sauce, top with cheese and grill?
4. Or put cold chicken in with hot pasta and put under grill with cheese? (am suspecting this last way is most likely to cause food poisoning but not sure)

I am notorious for overcooking meat as I am paranoid about food poisoning as was vegetarian through my teens and twenties so never learned how to cook meat properly. Not helped by the fact my mum and grandma always overcook it as they both are worried about salmonella etc!

TIA!

I would say 1 or 3, but would probably do 1.

As long as it is reheated properly I wouldn't worry.

Thank you! Think I will probably go for 1 too. Next question- how do I know it's hot enough without trying it?! And without going the cook-til-any-nutrition-value-has-gone route?