Soak the cashews in a bowl of boiling water for 15 minutes. Drain and set aside.

In a blender, combine soaked cashews, tofu, lemon juice, and zest. Blend until creamy, about 1-2 minutes. Refrigerate for 30 minutes.

Slice the red onions and mix with olive oil, vinegar, lemon juice, sumac, salt, and parsley. Let marinate for 10-15 minutes.

Slice heirloom tomatoes and mix with olive oil, minced garlic, parsley, basil, and lemon juice. Let sit for 5-10 minutes.

Spread the tofu mixture on one side of each slice of bread. Layer marinated tomatoes and onions, then top with lettuce if desired.

Close the sandwich and serve immediately for peak freshness.