01 - Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease a baking dish.
02 - Slice zucchini in half lengthwise. Carefully scoop out the center flesh with a spoon, creating a 1/2 cm thick shell. Reserve the scooped flesh and chop it finely.
03 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook for 2-3 minutes until translucent. Add minced garlic and cook for an additional 30 seconds.
04 - Add the diced bell pepper and the reserved chopped zucchini flesh to the skillet. Cook for 3-4 minutes until the vegetables have softened.
05 - Add ground beef or turkey to the skillet. Cook, breaking up the meat with a spoon, until it is completely browned and cooked through.
06 - Stir in dried oregano, dried basil, salt, black pepper, red pepper flakes (if using), and the drained diced tomatoes. Simmer for 5 minutes until the mixture has slightly thickened. Remove from heat.
07 - Arrange the zucchini halves cut-side up on the prepared baking sheet. Evenly distribute the prepared filling among the zucchini boats.
08 - Evenly sprinkle the shredded mozzarella and grated Parmesan cheeses over the stuffed zucchini.
09 - Bake for 20-25 minutes, or until the zucchini is tender and the cheese topping is melted and golden brown.
10 - Remove from the oven, garnish with fresh chopped basil or parsley, and serve warm.