Preheat oven to 400 degrees F. If you are putting them on the BBQ grill, preheat the grill to high heat.
Cut off the tops of the tomatoes at the stem end, then scoop out the seeds and spines. I use a melon baller for this. Place the hollowed-out tomatoes cut side down on a paper towel lined plate.
For the stuffing, place the bread crumbs in a large bowl and melt the butter in a skillet over medium-high heat. Add the onion and garlic and cook until the onion is just soft; about 3 minutes.
Add the onion/butter mixture to the bread crumbs then add the parsley, cheese, salt and pepper. Mix well.
Fill each tomato cavity with the stuffing mixture, letting it mound up on the top.
Bake or grill about 5-10 minutes or until the tomato is just beginning to get soft. If you want more browning on the top of the stuffing, pop them under the broiler for a minute or two.