Heat oven to 425°.
Toss the diced potatoes and sweet potatoes with 2 tbsp. olive oil, salt, pepper, and rosemary. Spread in a single layer on a large, lined baking sheet. Roast for 25 minutes, stirring halfway.
When the potatoes come out of the oven, start cooking the rest of the veggies.
Heat the remaining 2 tbsp. olive oil in a very large skillet over medium heat. When hot, add the onions and green peppers. Season with salt, black pepper, garlic powder, cumin, smoked paprika, and crushed red pepper. Stir regularly until the onions are beginning to brown.
Add the roasted potatoes and continue to sauté another 2–3 minutes.
Add in the riced cauliflower and kale, stirring until the kale is wilted and the cauliflower is beginning to brown.
Season the pan with white wine vinegar and fresh thyme. Stir to combine. Taste and adjust salt and pepper as needed.