Cook pasta in a saucepan of boiling salted water, stirring often, until al dente. Drain, then rinse with cold water until it's cool. Transfer pasta to a large salad bowl. Add oil, onion, vinegar, mustard and salt, then toss well.
Crisp bacon in microwave, according to package directions; break into 1-inch pieces. Add to pasta with spinach, tomatoes and Parmesan cheese. Toss well and serve.