In a medium skillet, heat the vegetable oil or butter over medium heat.
Add the finely chopped onion and sauté until it becomes translucent, about 3-4 minutes.
Add the minced garlic and continue to sauté for another minute.
Add the chopped tomatoes and bell pepper (if using). Cook until the vegetables are softened and most of the liquid from the tomatoes has evaporated, about 5-7 minutes.
In a bowl, crack the eggs and beat them lightly with a fork. Season with salt and black pepper to taste.
Reduce the heat to low and pour the beaten eggs into the skillet with the cooked vegetables.
Stir gently and continuously, allowing the eggs to cook slowly and mix with the vegetables.
Continue to cook until the eggs are set but still moist, about 3-5 minutes. Do not overcook, as perico should be soft and slightly creamy.
Transfer the perico to a serving plate.
Garnish with chopped fresh cilantro or parsley if desired.
Enjoy your meal!