Pat the tofu dry using paper towels and cut into ¾-inch cubes.
In a small bowl, whisk together canola oil, half of the grated garlic, and 1 tablespoon soy sauce.
Pour one-third of the marinade into a shallow dish, then add the tofu. Pour the remaining marinade over the tofu and gently toss to coat. Let marinate for 45 minutes.
In another bowl, whisk together peanut butter, lime juice, agave nectar, remaining soy sauce, ginger, sriracha, sesame oil, and remaining garlic. Add 1–3 tablespoons hot water until smooth.
Preheat the air fryer to 400°F (200°C).
Coat each tofu cube evenly with cornstarch, shaking off any excess.
Arrange tofu in a single layer inside the air fryer basket.
Cook for 15–18 minutes, shaking the basket twice during cooking, until golden and crispy.
Toss warm soba noodles with spinach and the prepared peanut sauce.
Top the noodles with the crispy Air Fryer Tofu with Peanut Sauce and serve immediately.