Preheat the Air Fryer: Set your air fryer to 350°F (175°C) and preheat it for about 3 minutes.
Prepare the Tomato Base: In a bowl, mix the tomato paste, chopped onion, minced garlic, water, and 1 tablespoon of olive oil. Season with salt and pepper to taste. Pour this mixture into the bottom of an air fryer-safe baking dish that fits in your air fryer basket.
Layer the Vegetables: Arrange the slices of eggplant, zucchini, yellow squash, red bell pepper, and yellow bell pepper in alternating layers, working from the outer edge of the dish towards the center. Slightly overlap each slice for a nice visual effect.
Drizzle with Oil and Season: Drizzle the remaining 3 tablespoons of olive oil over the vegetables and sprinkle with salt, pepper, and fresh thyme leaves.
Cook in the Air Fryer: Place the baking dish into the air fryer basket. Air fry at 350°F (175°C) for 20-25 minutes, checking for doneness halfway through. If the vegetables start to brown too much, you can cover them with a small piece of parchment paper or foil to prevent over-browning.
Final Check: The vegetables should be tender and lightly roasted when done. If they need more time, cook for an additional 3-5 minutes, depending on your air fryer model.
Serve: Once cooked, remove the dish from the air fryer and serve the tian with dollops of mascarpone cheese on top for extra creaminess. Enjoy as a side dish or a light meal!