Bring a large pot of water to a boil and add the beets.
Cook until almost tender, about 20–25 minutes.
Add the Michigan apples during the last 5 minutes of cooking.
Drain and rinse with cold water.
Transfer beets, apples, and purple onion to a large bowl.
Add lemon juice + zest, Dijon mustard, salt, parsley, cilantro, za’atar, and olive oil.
Toss everything really well and let it marinate for 1–3 hours so the flavors fully come together.
Arrange arugula on a large serving platter.
Spoon the beet + Michigan apple mixture over top and finish with crumbled feta.
