Preheat your oven to 400°F (200°C).
Slice the zucchinis in half lengthwise and scoop out the center using a spoon to create boats.
In a mixing bowl, combine the shredded chicken, BBQ sauce, garlic powder, and black pepper. Mix well until the chicken is fully coated.
Drizzle the olive oil over the zucchini boats and place them cut-side up on a baking sheet.
Fill each zucchini boat with the BBQ chicken mixture, pressing it down gently to pack it in.
Top each filled zucchini boat with shredded cheddar cheese and diced red onion.
Bake in the preheated oven for 20-25 minutes, or until the zucchinis are tender and the cheese is melted and bubbly.
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley if desired before serving.