Preheat your oven to 375°F (190°C).
Slice the zucchinis in half lengthwise and scoop out the seeds.
Drizzle olive oil over the zucchini halves and season with salt and pepper.
In a skillet, heat olive oil and sauté onions and garlic until softened.
Add diced tomatoes and bell peppers, and mix in the cooked quinoa or rice.
Stir in shredded cheese until melted.
Fill the zucchini boats with the mixture.
Place in a baking dish and bake for 25-30 minutes.
Remove from oven and let cool for a few minutes.
Garnish with fresh herbs before serving.