Cook spaghetti in salted water according to the package directions. Drain, rinse with cold water and toss with 1½ tablespoons sesame oil. Pour into large bowl.
Combine peanut butter, 1½ tablespoons sesame oil, soy sauce, water, rice vinegar, honey, and chili garlic sauce in a food processor. Blend until smooth. Pour over spaghetti. Add cucumber, tofu, and half the cilantro. Gently toss. Transfer to serving platter. Sprinkle with remaining cilantro and peanuts.