i used goat's milk feta, tomatoes, kalamata olives & fresh thyme, seasoned with sea salt and freshly ground black pepper. i also drizzled olive oil over the filling before closing it up. as an additional note, i brushed the bread with olive oil but it's not necessary. it browns perfectly well without it.
if you are making the sandwich in a frypan, use something to weigh it down. you can use a pot filled with water halfway on either side making sure it doesn't tip or a brick of some sort if you have one. lodge even sells a cool preseasoned cast iron sandwich press.
fill the sandwich.
over medium heat, in dry fry pan toast the sandwich for a good 5 to 7 minutes, making sure it's weighted down.
flip over and repeat process.