Cook the Spaghetti: Grab a big pot and cook your spaghetti according to package directions. Make sure you salt the water generously! You want the pasta to be cooked al dente, not mushy, since it will soak up dressing.
Cool Down the Pasta: This is key! Once the spaghetti is cooked, drain it really well. You can rinse it briefly with cold water to stop the cooking process faster, but make sure it's drained thoroughly. Transfer it to a large bowl and let it cool completely. You don't want warm pasta wilting your lovely veggies! I often do this step a bit ahead of time.
Prep Your Veggies: While the pasta is cooking and cooling, get chopping! Halve your cherry tomatoes, dice your cucumber, green pepper, and red pepper, and finely chop that red onion. Try to keep the pieces roughly the same size so you get a bit of everything in each bite.
Combine Everything: Add all those beautiful chopped veggies to the bowl with the cooled spaghetti. If you're using them, toss in the sliced black olives and grated Parmesan cheese now too.
Add the Dressing: Pour that cup of zesty Italian dressing all over the pasta and veggies.
Toss and Season: Grab some tongs and gently toss everything together until the pasta and veggies are well coated in the dressing. Taste a little bit and add salt and freshly ground black pepper as needed. Remember, the dressing and cheese add salt, so start with a little and add more if necessary.
Chill Time: This is the hardest part – waiting! Cover the bowl and pop it in the fridge for at least 1 hour. This allows the flavors to meld together and the pasta to soak up some of that delicious dressing. Honestly, it's even better after a few hours, or even the next day!
Serve: Give it another quick toss before serving. Enjoy your amazing, easy spaghetti salad!