Cook the spaghetti in a large pot of salted boiling water according to package directions until al dente. Drain and rinse under cold water until completely cool, then let drain thoroughly.

While the pasta is cooking, prepare the vegetables: halve the tomatoes, dice the cucumber and bell pepper, and finely chop the red onion.

In a large mixing bowl, combine the cooled spaghetti with the vegetables.

Pour in the Italian dressing and add the Parmesan, Italian seasoning, garlic powder, salt, and black pepper. Toss gently until everything is evenly coated.

Taste the salad and adjust seasoning if necessary. Cover and refrigerate for at least 2 hours before serving, or longer for better flavor.

Toss again before serving and add more dressing if needed.