Measurements provided are a guide, feel free to use a little less or a little more depending on preference.
MAKE IT VEGAN: Omit the cheese.
MAKE IT DAIRY FREE: Omit the cheese.
MAKE IT NUT FREE: Use sunflower seeds instead of walnuts.
MAKE IT PORTION FIX APPROVED: Use colored containers to measure out ingredients. This salad works perfectly as a blue (half feta, half chopped walnuts), purple (half apple, half blueberry) and green.