Prepare the Potatoes:
Preheat your oven to 180°C (350°F).

Peel and slice the potatoes into thin rounds. Toss them with olive oil, salt, black pepper, Provencal herbs, and sweet paprika.
Spread the potatoes in a greased baking dish and bake for 30 minutes until slightly tender.
Prepare the Eggs:
In a bowl, whisk the eggs with a tablespoon of mayonnaise. Season with salt and ground black pepper.
Prepare the Vegetables:
In a pan, heat a little olive oil and sauté the chopped onion until translucent.

Add minced garlic, grated carrot, and chopped red bell pepper. Season with salt, black pepper, and paprika. Cook until the vegetables are soft.
Prepare the Sauce:
In a saucepan, melt the butter over medium heat. Stir in the flour and cook for 1-2 minutes to form a roux.

Gradually add the milk, whisking constantly to avoid lumps. Cook the sauce until it thickens, then season with salt and black pepper.
Assemble the Casserole:
Take the partially baked potatoes out of the oven. Pour the egg mixture evenly over the potatoes.

Layer the sautéed vegetables and sliced sausages on top.
Pour the prepared sauce over the casserole and sprinkle with grated mozzarella cheese.
Bake:
Return the casserole to the oven and bake at 180°C (350°F) for another 30 minutes, until the top is golden and bubbly.
Garnish and Serve:
Sprinkle chopped green onions on top before serving. Enjoy the casserole hot.