3 tablespoons olive oil
1 large zucchini, finely diced
1 red bell pepper, finely diced
1 yellow pepper, finely diced
5 cloves garlic, smashed to a paste with coarse salt
1/2 teaspoon red pepper flakes, divided
Salt and freshly ground black pepper
2 large eggs, lightly beaten
1 tablespoon finely chopped fresh thyme leaves
1/4 cup chopped fresh parsley leaves, plus more for garnish
1/2 pound ground pork
1/2 pound ground veal
1 pound ground beef chuck
1 cup panko (Japanese) bread crumbs
1/2 cup freshly grated Romano or Parmesan
1 cup ketchup, divided
1/4 cup plus 2 tablespoons balsamic vinegar