Pre-heat oven to 350F, lightly brush both sizes of the zucchini with olive oil and place on a foil-lined baking sheet. Cook ground beef and onions until the onions are see-through, add to the zucchini boats. Mix cheese and herbs together in a small bowl and sprinkle over the zucchini along with salt and pepper to taste. Bake for 15 minutes and place under the broiler for the last 3-5 minutes until cheese is crispy and browned.