Mix the tomato with the mashed avocado in a medium bowl.
Stir in the chili, coriander and a squeeze of lime.
Taste a little of the mixture and add salt and pepper to taste.
Spread the inside of one slice of bread with the avocado and tomato mixture.
Top with two slices of cheese.
Place the second slice of bread on top.
Brush the outside of both pieces of bread with olive oil. (You can use softened butter if you prefer.)
Toast in a frying pan over medium heat, turning carefully once, until golden brown on both sides.