01 -
Preheat oven to 175°C. Lightly grease a 23-cm pie plate or similar-sized baking dish.
02 -
Heat olive oil in a small skillet over medium heat. Sauté diced onion until soft and translucent, about 3–4 minutes. Set aside to cool slightly.
03 -
In a medium bowl, combine shredded cheddar, mozzarella, grated Parmesan, mayonnaise, garlic powder, dried basil, dried oregano, and the cooked onion. Mix well until thoroughly incorporated. Season to taste with salt and black pepper.
04 -
Arrange tomato slices in overlapping layers in the prepared baking dish.
05 -
Spread the cheese mixture evenly over the tomatoes, ensuring full coverage.
06 -
Bake for 25–30 minutes, or until the top is golden brown and bubbly.
07 -
Allow to cool for 5–10 minutes, then garnish with fresh basil before serving.