Make vinaigrette: Purée all vinaigrette ingredients in a blender. Reserve 1 cup vinaigrette for marinating tofu.
Marinate tofu: Combine reserved vinaigrette and soy sauce in a sealable plastic bag. Add tofu, seal bag, and turn to coat. Marinate, chilled, turning bag over occasionally, at least 30 minutes and up to 1 day. Bring to room temperature, about 30 minutes, before grilling.
Cook wheat berries: Simmer wheat berries in unsalted water in a 2- to 3-quart saucepan, partially covered, until tender but still chewy, 1 1/4 to 1 1/2 hours. Drain, then return to pan and stir in salt. Cool to room temperature.
Grill peppers, tomatoes, and tofu: Prepare grill for direct-heat cooking over hot charcoal.
Pour off marinade from tofu and pat dry, then transfer to a plate.
Thread tomatoes 1/4 inch apart onto skewers.
Oil grill rack and grill bell peppers, covered only if using a gas grill, turning occasionally with tongs, until skins are blackened, 10 to 12 minutes. Transfer to a bowl, then cover and let steam 10 minutes.
Grill tomatoes, covered only if using a gas grill, turning over once, until blistered and softened, 3 to 4 minutes.
Oil grill rack well, then grill tofu, covered only if using a gas grill, until grill marks appear, about 3 minutes. Loosen tofu with a metal spatula, then turn over and grill until heated through and grill marks appear, about 3 minutes more. Transfer to a clean plate and cover.
Assemble salad: Stir together tomatoes, celery, scallions, olives, wheat berries, and 1/2 cup vinaigrette. Let stand, uncovered, 15 minutes.
Peel and seed peppers, then cut into 1-inch-wide strips. Stir into wheat-berry mixture.
Halve pieces of tofu diagonally (for a total of 8 triangles).
Toss lettuce and mint on a platter, then top with wheat-berry mixture and tofu. Drizzle with some vinaigrette; serve remainder on the side.
Cooks' note: If you aren't able to grill outdoors, you can cook the tofu and tomatoes in a hot lightly oiled well-seasoned large (2-burner) ridged grill pan. Bell peppers can be broiled on rack of a broiler pan about 2 inches from heat, turning over once, 10 to 20 minutes.