Soak cashews in boiling water for 15 minutes. Drain and blend with tofu, lemon juice, and zest until smooth. Refrigerate for 30 minutes.

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

Slice heirloom tomatoes and drizzle with remaining marinade ingredients. Let sit for 5-10 minutes, turning occasionally.

Spread tofu mixture on one slice of bread, layer with marinated tomatoes, sumac onions, and lettuce. Top with another slice of bread spread with tofu mixture.

Slice the sandwich in half and serve immediately, optionally with chips or salad.