1) Preheat oven to 375 degrees. Cut butternut squash and potatoes in bite size halves or chunks. In a large bowl, mix squash and potatoes with olive oil (not extra virgin olive oil) or avocado oil, balsamic vinegar, spice mix (optional), and salt and pepper.
2) Peel red onion and cut into wedges so the layers stay together if possible. This is so they can cook at a similar length of time as the potatoes and squash. If the red onion is large, you may want to cut the wedges in half lengthwise so they are a similar size as the potatoes and squash. Gently mix in a bowl with oil and salt and pepper.
3) Pour everything cut, oiled, and seasoned, onto large sheet pans. Give the sheet pans a shake so the vegetables spread out and are not on top of each other.
4) Place pans in hot oven and roast until tender and golden brown. Place pans under a broiler one at a time if you wish to add a little more browning, but DON'T LEAVE THE BROILER UNDER ANY CIRCUMSTANCE.