Melt butter in a medium frying pan over medium heat. Add onion and pear. Cook, stirring occasionally, until soft, about 5 minutes. Sprinkle with sugar, turn heat to low, and cook until light brown, about 10 minutes. In a small bowl, combine mayonnaise, sour cream, and blue cheese.
Salt and pepper both sides of the steaks. Heat a large frying pan (not nonstick) over medium-high heat. Add the oil, let heat until rippling, and put in steaks. Cook steaks until they can be turned easily, about 4 minutes. Turn over and cook 4 to 6 minutes. Transfer to a cutting board and let rest 10 minutes.
Meanwhile, wipe oil from frying pan and warm tortillas, one at a time, over low heat.
Thinly slice steaks. Spread about 2 tbsp. blue-cheese dressing on each tortilla, leaving a 1-in. margin on all sides. Top each with 1/2 cup spinach leaves, 1/4 of the steak slices, and 2 tbsp. onion-pear relish. Fold bottom inch of tortillas over ?fillings and fold over sides to form wraps.
Note: Nutritional analysis is per serving.