Brown the ground beef or sausage, drain. Preheat the oven to 350°.
While the meat is browning, slice the zucchini in half lengthwise. Scoop out the flesh leaving a ¼-inch shell. Roughly chop the zucchini flesh. and add to the drained ground beef.
To make the filling, combine the meat and chopped zucchini, the marinara, Italian seasoning, onion powder, pepper flakes, garlic powder, parmesan, ¾ cups of panko, and one cup of mozzarella. Salt and pepper to taste.
Arrange the zucchini shells in a casserole dish in a single layer. Lightly season the empty shells with salt and pepper. Fill the shells generously with the meat mixture. Cover the baking dish tightly with aluminum foil. Bake for 45 minutes or until you can pierce a zucchini shell easily with a fork.
When the zucchini is tender, remove the foil. Sprinkle the remaining cup of mozzarella over the stuffed zucchini. Toss the remaining panko crumbs with a teaspoon of olive oil and sprinkle evenly over the zucchini. Return to the oven long enough to melt the cheese and brown the bread crumbs, about 10 minutes. Let the zucchini rest for 5 minutes before serving.
