Soak the cashews in hot water to cover in a heat-proof container for at least 15 minutes, or the sunflower seeds for 10 minutes if you do not own a high-speed blender. Drain and set aside.
Blend: Transfer the cashews, basil, miso, garlic, lemon juice, and water to the canister of a high-speed blender. Blend on high until smooth.
Mash: Transfer the chickpeas to a large bowl. Add the green sauce and hemp hearts (if using). Mash the chickpeas and mix until the desired texture.
Optional: Toss the arugula with a drizzle of olive oil, balsamic vinegar, and salt to taste.
Make sandwiches: Place one-fourth of the mashed chickpea mixture on toasted bread. Top with one-fourth of the arugula. Top with toasted bread or serve open-faced.
Notes
Add more chickpeas to the sauce as desired.
Storage: Refrigerate the chickpea sandwich filling in an airtight container for up to 5 days.