Heat olive oil in a skillet over medium-low heat; cook and stir onion with a pinch of salt until lightly browned and caramelized, 10 to 15 minutes. Add figs and balsamic vinegar to onion; cook over medium heat until vinegar is reduced by half, about 5 minutes. Season fig mixture with salt and pepper.
Spread spinach onto serving plates and top with fig mixture and Gorgonzola cheese.