Preheat your oven to 400ºF (200ºC) and lightly grease a 10-inch cast-iron skillet with olive oil. Sprinkle 1 cup of panko bread crumbs evenly on the bottom.

In a medium skillet, heat 2 tablespoons of olive oil over medium heat. Add chopped red onions and sauté for about 4-5 minutes until tender. Stir in minced garlic and crushed red pepper flakes, cooking for an additional minute. Pour in 1/4 cup of dry red wine and cook until almost dry, about 1-2 minutes.

Spread the sautéed onion mixture evenly across the bottom of the prepared skillet.

Slice the butternut squash, russet potatoes, zucchini, and tomatoes into 1/4-inch-thick rounds.

Layer the sliced vegetables in stacks, alternating colors and types, in a circular pattern around the skillet. Drizzle freshly squeezed lemon juice over them.

Sprinkle the layers with herbes de Provence, sea salt, and coarsely ground pepper. Cover with aluminum foil and bake for about 1 hour.

Mix 1 cup of shredded Gruyere cheese, the remaining panko, and 2 tablespoons of melted clarified butter or ghee until well combined.

Carefully remove the foil and sprinkle the cheese mixture evenly over the vegetables. Bake for an additional 15 minutes.

Allow the Vegetable Tian to rest for about 10 minutes before slicing and serving.