I love paninis in the summers, they remind me of being a kid in Cyprus in the summers when we used to come back to the beach condo from the sea and sit dripping wet on the patio while we basically ate these. I'm sure there was other food, but this is what I remember.
I used the forman grill to make them, some people I'm sure own panini presses, if you dont have either, you want to frying pans, you heat both and place the sandwich in one, heat one side, flip over and place the other heavier pan on top, to get it to press down, there are other methods involving bricks and if you have bricks laying around at your house I'm sure that should work even better. All of ours are in the non-functioning fireplace.
There are a few other tricks I have when it comes to paninis, but this is the most basic kind, you want to butter the bread on the outside, or use a little cooking spray, and if you're going to add anything afterwards, you want to have the layer of ham on bread, so you can in fact open the sandwich, if you're not adding anything, then place cheese on both sides and everything will be glued together.
I assemble the sandwich on the grill, I start with buttered bread, butter side down, then add ham, then cheese then the second layer of bread buttered side up.
After it's done, and you have the coloring on the bread you're looking for, pry apart the side with the ham and add a little sliced avocado, Creamy, cheesy heaven.
2 slices multigrain bread
1 slice ham
1 slice swiss cheese
1/4 avocado, sliced
Speaking of using avocado, I have tried many methods keeping the fruit from turning brown, but the best method seems to be that press and seal stuff, I apply it directly to the fruit, having it actually touch the green, and getting out all the air, and it stays so pretty.