Place quinoa in Multipurpose Steamer; stir in 1 cup hot water. Microwave on high, uncovered, until tender and water has been absorbed, 12–15 min.
Meanwhile, grate and measure out 1 cup zucchini. Wash and separate lettuce leaves. Set aside.
In a small bowl, combine mayo, Big Burger Sauce Mix, ketchup, and relish. Set aside.
In a separate bowl, combine Veggie Burger Mix with 1⁄2 cup hot water. Using the 2-in-1 Citrus Press, squeeze in 3 tbsp juice from lemon. Add zucchini; stir until combined. When cooked, stir in quinoa.
Preheat large fry pan over medium heat. When hot, add oil; scoop batter onto pan, making four burgers. Lightly press and flatten into shape. Cook until golden brown, 3−5 min per side.
Divide half the lettuce leaves on plates; add a dollop of Big Burger Sauce. Cover with patties and toppings, then remaining lettuce. Add toppings, if desired.