Preheat the oven to 400ºF. Heat the olive oil in a large cast iron skillet over medium-high heat, and saute the garlic and onion until the onion is translucent, but not brown, about 5 minutes.
Chop the fresh spinach, to help it fit in the pan. You may need to add the spinach in large handfuls, then cover briefly for 30 to 60 seconds with a lid, to help it shrink down. I usually do this in 3 batches for a 5-ounce bag of fresh spinach. If you're using thawed frozen spinach instead, be sure to squeeze out excess moisture before adding it to the pan.
Chop the artichokes into tiny pieces, then add them to the pan with the other veggies. Season with 1/2 teaspoon of salt, and stir well.
Turn off the stove top while you make the cashew sauce. In a high-speed blender, add the cashews, water, lemon juice, vinegar, and 1 teaspoon of salt. Blend until very smooth, then pour over the veggies in the pan.
Stir well, to make sure the vegetables are evenly distributed in the sauce. Transfer the skillet to the preheated oven, and cook until everything is hot and the sauce looks thicker, about 15 minutes.
Serve warm, with your favorite chips, bread, or sliced veggies for dipping. Leftover dip can be stored in an airtight container in the fridge for up to 5 days. I like this dip cold, but if you reheat it, you might need to add an extra splash of water, to help thin out the sauce again.
Nutrition information is for 1/8 of this whole recipe, which is about 1/4 cup. This information is just an estimate, and not a guarantee.