Heat the oil in a large nonstick pan over medium heat. Add the onion and cook, stirring occasionally, until onion is dark golden brown, about 5-10 minutes. Remove from pan.
Rinse your spinach and add the wet leaves to the pan; cook 2 minutes, or until spinach is just wilted. Remove from skillet and turn off heat.
Sprinkle a quarter of the goat cheese on one side of each tortilla and top with spinach, tomato and onion; fold closed and press lightly. Heat a clean pan and place two folded quesadillas in it; cook two minutes per side, or until golden brown. Repeat.
*If using the Tortilla Land uncooked tortillas, first brown one side of the tortilla in the clean pan. Flip it over, fill half with the cheese, spinach, tomato and onion, then fold the tortilla in half. Cook for about a minute and then flip it over to cook the other half for another minute or until lightly browned.