Preheat the oven to 450°F.

Slice tomatoes in half then scoop out and discard the pulp and seeds. Sprinkle with 1/4 teaspoon salt then turn the tomatoes upside down on a sheet pan lined with a wire rack to extract juices, about 15 minutes. Discard the juices.

In a medium-size mixing bowl, combine the panko breadcrumbs, Parmesan cheese, yellow onion, parsley, garlic, remaining 1/4 teaspoon salt, and ground black pepper.

Stuff the tomatoes with the bread crumb mixture then bake 10 minutes, until topping is golden in color, then serve.