Preheat oven to 350°F (175°C). Line an 8"x8"x2" baking dish with parchment paper and set it aside.
Place the bread cubes on an unlined baking sheet and bake for 10 minutes. Remove from the oven and transfer to a large mixing bowl, set aside for now.
Drain the cashews and place them in your blender (discard the soaking water), along with the non-dairy milk, nutritional yeast, arrowroot flour, salt, onion powder, black pepper, oregano, and cayenne. Blend until perfectly smooth then set aside for now.
Heat a skillet over medium heat for 2 minutes. Add the leeks and saute for 5 minutes, adding a splash of water if they stick. Stir in the spinach and garlic and cook for 2 minutes, until the spinach has wilted. Stir in the chopped artichoke hearts, peas, basil and dill, then remove the skillet from the heat and allow to cool for a few minutes.
Transfer the vegetables to the mixing bowl with the bread cubes and toss together. Give the non-dairy milk mixture a quick blend, about 3 seconds, then pour it over everything in the bowl and toss to coat. Transfer the mixture to the parchment-lined baking dish and let it rest for 10 minutes.
Place the dish, uncovered, into the oven and bake for 45 minutes.
We suggest serving with a cheesy sauce (recipe below) and a side of fruit.