Prepare the Tofu: Pat the pressed tofu dry. Crumble into a bowl. Add lemon juice, oregano, and salt; toss gently. Let stand 10–15 minutes.
Make the Vinaigrette: In a small bowl or jar, whisk olive oil, lime juice, sumac, lime zest, garlic, salt, and black pepper until emulsified.
Build the Salad: Gently blot watermelon cubes with paper towels to reduce excess juice. On a large platter, arrange watermelon, chickpeas, cucumber, and red onion.
Layer and Dress: Drizzle about half the vinaigrette over the base. Scatter avocado and the herbed tofu crumbles on top. Add torn herbs and jalapeño, if using.
Serve: Drizzle the remaining vinaigrette. Taste and adjust with a pinch more salt or a squeeze of lime, then serve immediately.