Preheat oven to 350 degrees Fahrenheit. Spray a 1-quart baking dish with cooking spray.
Warm 1 tablespoon olive oil over medium heat in a large saucepan. Add onions and cook, stirring often, until tender and translucent.
Add garlic powder, nutritional yeast, cayenne pepper, Dijon mustard, lemon juice, and salt. Stir to combine. Add vegetable broth followed by cashews. Bring to a simmer, then reduce heat and simmer for 8-10 minutes to allow cashews to soften.
While cashews are simmering, add arrowroot starch and water to a small bowl or glass measuring cup. Stir to combine to make a slurry. Set aside.
Carefully, transfer the cashews and vegetable broth mixture to a high speed blender. Add arrowroot slurry. Blend until completely smooth, stopping periodically if needed to wipe down sides. Set aside.
Add remaining olive oil to saucepan over medium heat. Add garlic and allow to cook about 1 minute until fragrant. Add spinach and cook until heated through. Add artichokes. Remove from heat.
Transfer cashew mixture back into saucepan. Stir until ingredients are evenly incorporated. Salt and pepper as desired.
Transfer dip into prepared baking dish and bake for about 20 minutes. If you want a slightly browned top, turn the broiler on high at the end of baking and broil for 1-2 minutes.
Remove from oven and serve immediately with chips or crackers.