Step 1

Arrange a rack in the middle of the oven and heat the oven to 400°F. Meanwhile, drain and press the tofu. Wrap the block in a few layers of paper towels, then set on a dinner plate. Weigh it down with a heavy object such as a skillet, pot, or large can, and let sit for at least 15 minutes to drain. Thinly slice 1/2 small red onion and place in a bowl of ice water (this will take off its bite); set aside.

Step 2

Make the falafel seasoning: Place the 1 teaspoon garlic powder, 1 teaspoon ground cumin, 3/4 teaspoon ground coriander, 3/4 teaspoon kosher salt, 1/4 teaspoon freshly ground black pepper, and a pinch of cayenne pepper in a medium bowl and stir to combine. Add the 2 tablespoons olive oil and stir to combine.

Step 3

Tear the pressed tofu into bite-size pieces, then add — along with any small crumbles of tofu — to the seasoning and gently stir to evenly coat. Lightly coat a rimmed baking sheet with olive oil (about 1/2 tablespoon), then add tofu and spread into an even layer. Roast for 20 minutes. Flip the tofu and roast until golden and crispy all over, 10 to 15 minutes more. Meanwhile, make the whipped tahini.

Step 4

Make the whipped tahini: Finely grate the zest of half the lemon and place in a food processor fitted with the blade attachment. Cut the lemon in half, then squeeze the juice from one half into the food processor (about 1 1/2 tablespoons). Add 1/2 cup well-stirred tahini. Process, scraping down the sides and bottom of the bowl if the tahini gets stuck, until it begins to aerate, 5 to 7 minutes. With the motor running, slowly stream in 1/4 cup cold water. Scrape down the sides and add 1/2 cup plain yogurt and 1 teaspoon harissa paste. Process until smooth. Taste and season with salt (you'll likely need about 1/2 to 3/4 teaspoon kosher salt). If you'd like a spicier tahini, add more harissa 1/4 teaspoon at a time.

Step 5

Thinly slice the Persian cucumbers and slice the reserved lemon half into wedges. Drain the onion. Divide whipped tahini between 4 plates or shallow bowls (you may not use it all). Top with the tofu, cucumber, onion, and torn herbs. Serve with lemon wedges, and torn soft pita, for mopping up any extra tahini.