Heat the oven to 400°.
Heat 1 tablespoon oil in a large skillet over medium heat. Add the Italian sausage (squeezing the meat out of the casings, if using links) and saute until browned, about 8-10 minutes. Use a slotted spoon to remove the sausage to a medium mixing bowl, leaving the fat in the pan.
If the pan is still looking a little dry, add one more tablespoon oil. Add the mushrooms and 1/4 teaspoon salt and saute, stirring occasionally, until deeply browned and most of the moisture in the pan has evaporated, about 10-12 minutes.
While the mushrooms are cooking, peel and dice the onion and de-seed and chop the pepper.
Once the mushrooms are ready, add another tablespoon of oil, if necessary. Then add the onion and pepper to the pan with another 1/4 teaspoon of salt. Saute until the onion and pepper are tender, stirring occasionally, about 5 minutes.
Meanwhile, in a large bowl whisk the eggs with the pizza sauce, nutritional yeast (if using), garlic powder, dried oregano, black pepper and 1/2 teaspoon salt.
Add the sausage and veggies to the egg mixture, along with the drained, sliced olives.
If the pepperoni slices are large, cut them in half or in quarters and stir into the egg mixture, making sure they don't stick together.
Grease a 9x13" baking dish with oil or an oil spray. Pour in the egg mixture and spread to an even layer.
Bake for about 30-35 minutes, until slightly bubbling and the top is set. Let cool for 10 minutes, slice and serve.