In a large pot heat the olive oil and add the chopped yellow onion and spring onions. Cook over medium heat for approximately 5 minutes, stirring occasionally to prevent the onion from burning.
Add the chopped parsley to the pot, and cook for about 2 minutes, stirring constantly.
Next add the potatoes to the pot along with the tomato sauce and 1 cup of water. Season with the salt and pepper. Bring to a boil and then reduce the heat to medium and cook, covered, for 20-25 minutes or until the potatoes are tender. Stir occasionally to make sure that the potatoes do not stick to the bottom of the pot. Do so carefully as to not break up the potatoes. If your pot is getting too dry during the cooking process, add a little more water, 1/4 cup at a time.
Add the chopped spinach, cover, and cook until the spinach is wilted, stirring occasionally.
Remove from heat, and let sit uncovered, for approximately 10-15 minutes, to allow the sauce to thicken.
Serve, and squeeze some lemon juice over each serving, if desired.