In a large skillet, heat the oil over medium heat. Add the pecans and cook about 3 minutes till golden. Remove the skillet from heat and using a slotted spoon, transfer the pecans to a plate.
To the oil in the skillet add the vinegar, sugar, salt and pepper. Stir till the sugar is dissolved. Remove skillet from heat.
Rinse and drain the beans. Drain the oranges. Thinly slice the onions.
In a large salad bowl, combine the spinach, beans, oranges and onions. Pour the dressing over the salad and toss well. Sprinkle the pecans on top.