Almost any vegetable can be dried and powdered! Good options include:
Roots: beets, carrots, sweet potatoes
Fruits: tomatoes, peppers, corn, zucchini, winter squash
Greens: kale, spinach, Swiss chard, cabbage
Others: onions, garlic, celery, herbs
Rinse produce well. Remove any bruised portions. Peel if desired. Slice, dice, or shred into small thin pieces to speed drying.