Cook the pasta to al dente, then drain and rinse under cold water to cool. Toss with a little oil.
Whisk together the mayo, mustard, lemon juice, salt, and pepper.
In a large bowl, combine the cooled pasta, corn, red pepper, greens, and red onion.
Pour over the dressing and toss to coat evenly.
Chill for at least 30 minutes, then taste, adjust seasoning, and serve.
Notes
Make extra dressing to refresh leftovers. Use vegan mayo to make it vegan and gluten-free pasta for a gluten-free version. Best made a few hours ahead.