Spray 1 slice of bread with avocado oil spray or butter
Place tuna, cheese, seasoning, and mayo on the bread.
Place the sandwich on the pan over medium heat for 2-3 min or until it's golden brown. Spray the top slice of bread with avocado oil spray (or more butter) before flipping it over.
Cook other side. If the cheese isn't melting yet, cover the pan, reduce the heat for 2 minutes until the cheese is oozing.