Soak cashews in boiling water for about 15 minutes. Drain and set aside.

In a high-speed blender, blend soaked cashews, nutritional yeast, miso paste, lemon juice and zest, oregano, and salt until smooth. Add plant-based milk and blend again.

In a skillet, heat olive oil and sauté shallot and garlic until fragrant. Add spinach, cook until wilted, then remove from heat.

In a bowl, combine mashed white beans, sautéed spinach, herbs, and half of the cashew cream. Chill for at least 30 minutes.

Toast whole grain bread slices. Spread mustard or pesto on them. Layer chilled filling and arugula between slices to assemble the sandwich.