Sauté onion in 2 tablespoons of the oil over medium heat for 20 minutes, until soft. Sprinkle with salt and place in a serving bowl.
Boil water in a small pot and stir in the couscous. Cover with a tight-fitting lid, and remove from heat. Let sit for about 12 minutes, until the water has been absorbed.
Place the couscous in the serving bowl with the onion. Add the mint, pecans, a tablespoon of olive oil, and vinegar. Toss gently to combine. Add salt and pepper to taste.
Serve warm, or allow to cool to room temperature.