1. Preheat oven to 350ºF.
2. Heat oil and butter in a 12-inch skillet over medium-high heat. Add shredded potatoes and cook for 5 minutes, scraping the bottom of the pan to keep them from sticking. Reduce to medium heat and add onion and peppers. Cook for another 4 minutes. Remove from heat and stir in spinach, tomatoes, salt, and pepper.
3. Make 7 wells in the vegetable mixture. Crack one egg in each well. Sprinkle a little more salt on each egg. Using hot pads, place skillet in oven. Bake 14 minutes for soft yolks or 18 minutes for hard yolks. Top with scallions and cilantro, if using, and serve immediately.