Preheat Oven to 375 degrees.
In a 10-12” nonstick skillet that’s at least 1-1/2 inches deep, heat the oil on medium high. While the oil is heating, slice the potatoes thinly, and lightly fry with oil and salt, turning once, do not burn. Remove and set aside.
Add the onions, peppers, mushrooms and garlic (if using) to the pan. Fry, stirring occasionally, until the onions are very soft and translucent.
In a large bowl, beat the eggs, 1/4 tsp. salt, and the pepper with a whisk.
Mix the cooked potatoes, onions, mushrooms, peppers and garlic and layer into a baking dish.
Pour the egg mixture onto the potatoes and spread.
Top with Parmesan cheese and bake for 30 minutes, until golden brown on the top.