If you are using fresh nopalitos, place them in a 1 quart saucepan, cover with water, and boil for about 7 minutes. Once they have turned to a drab green color, remove the nopalitos from the heat, and drain the water. If you are using jarred nopalitos, skip cooking them, and simply drain before using.
Heat the vegetable oil over medium heat in an 8” skillet. Add the onion and sauté until the onion is translucent, about a minute. Add the nopalitos, and sauté for another 2 minutes. Add the tomato, season with salt and pepper, and allow to simmer for about 2 minutes, until the tomatoes have become soft. Set aside.
In a separate bowl, scramble the eggs. Pour the eggs into the hot skillet, stirring well. Once the eggs are cooked, spoon the mixture into hot flour tortillas, top with nopalitos and serve.