Absolutely to die for. Made this grilled cheese for dinner yesterday, and it was so good. We still had some caramelized onion left from French Onion Grilled Cheese recipe (see link below) we made a few days ago, then I made up this recipe by using up the leftover caramelized onion, basil pesto, sun-dried tomatoes, some chopped black olives and slices of Swiss cheese that we had in the fridge. I used olive oil to grill the sandwiches in a medium nonstick skillet, and the cheese was nicely melted and oozing out, the combination of these ingredients was so good. Nicely browned and crispy sandwich with cheesy and flavorful filling, seriously delicious!!