Pulse all the dressing ingredients together except the salt and pepper until smooth and creamy. Season to taste with salt and pepper. Refrigerate.
Make the salad:
Cook the spaghetti to al dente according to package directions. Drain and toss with a tablespoon of olive oil. Refrigerate until cooled.
In a large mixing bowl toss everything together except the salt, pepper and red pepper flakes.
Mix in the dressing a little at a time and toss until everything is evenly coated. Season to taste with salt and pepper and red pepper flakes, if desired.