Preheat the oven to 400ºF. Spray a large rectangle of foil with cooking spray.
Place the beets on the foil. Place a second sheet of foil over the beets and crimp the top and bottom sheets together to make a sealed packet.
Place on a baking sheet and roast for 50 minutes. Allow the beets to cool, but keep the oven set to 400ºF.
Arrange the sweet potatoes on a rimmed baking sheet. Drizzle with 1 tablespoon of olive oil and sprinkle with cumin and chili powder. Toss to coat.
Roast for 15 minutes. Turn with a spatula and roast for 10-15 minutes more, until tender. Cool.
When the beets are cool enough to handle, gently rub them to peel off the skins. Dice into ¼-½ pieces.
Add the spinach to a large bowl along with beets, sweet potatoes, bell pepper, chickpeas, scallions, and dates.
In a small bowl, whisk together the remaining 4 tablespoons of olive oil with the mint, lemon juice, garlic and salt. Pour over the salad and toss to coat. Gently fold in the avocado.
Divide among serving bowls and top each with an equal amount of chopped egg.