Whisk balsamic sauce, soy sauce and garlic in a small bowl.
Cut the feta in cubes. Heat 1 tablespoon oil in a large nonstick skillet over medium-high heat until it shimmers. Add the feta and cook, turning occasionally, until browned, 6 to 8 minutes. Transfer to a plate.
Return the skillet to the heat and add the remaining 1 tablespoon oil. Stir in onion, celery and ginger; cook, stirring often, until fragrant, about 1 minute. Add snap peas, snow peas and peas; cook, stirring often, until bright green, 2 to 3 minutes. Return the feta to the pan along with the suace mixture and walnuts; cook, stirring, until heated through, about 1 minute.
Per serving : 35 mg Cholesterol; 8 g Fiber