1. Combine lemon juice, salt, and pepper in bowl with fork. Add oils, then whisk or mix with fork until smooth, about 30 seconds. The dressing will separate after 5 to 10 minutes, so use immediately or cover and refrigerate; mix again before -tossing with greens.
2. Dress the mixed arugula and walnuts with 1/4 cup of the Balsamic Vinaigrette. Add more to taste, otherwise reserve vinaigrette for other use. Serve immediately.