1. Cook the pasta according to package directions.
2. While pasta cooks, heat 1 tablespoon olive oil in a large skillet. Add onion, and sauté over medium-high heat until tender and fragrant, about 3 minutes. Add salt, balsamic vinegar, sun-dried tomatoes, crushed red pepper, and pine nuts; cook, partially covered, over medium-low heat for 4 minutes, stirring occasionally.
3. When al dente, drain the pasta and add it to the skillet, stirring to combine for about 1 minute. Transfer the pasta to a large serving bowl, and toss in the feta cheese, basil, and remaining olive oil. Serve immediately.