Cut the eggplant into thin slices and cherry tomatoes into halves. Then, place them on a baking sheet, season with salt and pepper then drizzle lightly with olive oil and dried basil.

Roast in the preheated oven (180°C/356°F) until the eggplants are golden and the tomatoes are blistered, approximately 20-25 minutes. Set aside.

Slice onions thinly. Heat the pan over medium heat; add the olive oil, onions and salt.

Cook slowly, while stirring occasionally, until the onions are golden brown and fragrant, about 20-30 minutes. Set aside.

In a small bowl, mix crème fraîche with freshly ground black pepper and a pinch of salt until well combined. Adjust the seasoning according to taste.

Brush the gluten-free bread slices with olive oil and dried basil. Toast lightly in a pan or bread toaster.

Spread a generous layer of the seasoned crème fraîche on one side of each bread slice.

On the other slice of bread, layer the fresh avocado slices, then the roasted eggplant slices, followed by the roasted cherry tomatoes. Spread a small amount of creme fraiche on each layer to keep the fillings together.

Add the caramelized onions evenly over the tomatoes. Carefully place the second slice of bread, spread side down, on top of the caramelized onion to complete the sandwich.