I love to make these. As pizzas go, they're cheap, quick and easy to make, and blumming tasty too.
A panini roll (two if you're feeling greedy or cooking for more than one), a tomato, some grated cheese. I cheat, given that you can buy cheese pre-grated nowadays.
Slice the panini roll in half, then slice up the tomato and place the slices on the panini.
Sprinkle grated cheese all over the panini/tomato combo. Doesn't matter if you spill some. Melted cheese is ace, whether it's on top of a panini or on an enamel plate. :-)
Place under the grill. The cheese needs to melt properly, and ideally (if you're anything like me) turn a nice shade of orange-y brown. Sometimes that's a trade-off between getting the cheese done to perfection and accidentally burning the panini.
Eat and, hopefully, enjoy!