Prepare Vinaigrette: Add all of the dressing ingredients to a mason jar or glass jar with a lid. Seal tightly and shake well until combined. Refrigerate until ready to use.
Cook Pasta: Bring a large pot of salted water to a boil. Cook the rotini according to the packet instructions, plus an additional 2 minutes. This helps keep the pasta soft once chilled rather than becoming firm and dry.
Drain and Cool Pasta: Drain the pasta in a colander and rinse under cold water for 10-15 seconds. Shake off any excess water, then transfer to a large bowl. Drizzle with a little olive oil and gently toss to coat. This helps prevent the pasta from sticking together as it cools, although you can skip this step if preferred. Set aside to cool completely.
Prepare Salad Ingredients: Drain and rinse the cannellini beans and drain the corn. Slice the cucumber and roughly chop the tomato. If your feta is sold in a block rather than pre-cubed, cut it into bite-sized cubes.
Assemble Salad: Add the cooled pasta, cannellini beans, corn, cucumber and tomato to a large serving bowl.
Dress Salad: Pour over about three-quarters of the vinaigrette and gently toss to combine. Add the feta cheese, then drizzle over the remaining dressing and gently toss again until everything is evenly coated. If making the salad a few hours ahead of time, I like to reserve about 1/4 of the dressing and drizzle it over just before serving for maximum freshness.
Serve: Serve immediately or cover and refrigerate until ready to serve. Give the salad a good toss before serving, as some of the dressing may settle at the bottom of the bowl.
Make Ahead Tip: If serving straight from the refrigerator, allow the pasta salad to sit at room temperature for 15-20 minutes before serving for the best texture. If making it a day ahead, reserve about 1/4 of the dressing and drizzle it over just before serving. If all the dressing has been absorbed, a squeeze of fresh lemon juice will help freshen and revive the salad.