Onions, carrots, peas and peppers, no. Try diced, dried, poblano chiles for a flavor spike. Dried poblanos are called chile anchos. I have never tried spinach so can't help there. I do a quick blanch with stuff like green beans, sugar snap peas, cabbage, broccoli stems and kohlrabi. Broccoli florets tend to turn to a paste on re-hydrating if blanched.

Generally though I find the most important thing when dehydrating is to cut the veggies into small pieces. I will buy packages of frozen mixed vegetables, diced carrots and small green peas and put them directly into the dryer. The results for mixed veggies are better if there are no green beans in the mix. Green beans can be pretty stiff long after the other stuff has re-hydrated. I give them an all day soak when I take them along. During the American Civil War, dried green beans were called "iron britches" and it was claimed that you could use them to nail a barn together.