1/2 large red bell pepper, finely diced (about 3/4 cup)
Over high heat, bring a sizable pot of salted water to a boil. For 7 to 8 minutes, boil the pasta until it is al dente. Drain thoroughly, then transfer to a bowl to finish cooling.
In the meantime, add the vegan sour cream, vegan mayonnaise, vinegar, parsley, mustard powder, and onion powder in a medium bowl. Whisk until well incorporated. The dressing should be covered and chilled until it is time to assemble.
When the pasta is totally cooled, combine it with the celery, peppers, and dressing. Use salt and pepper to season the food according to taste. Serve right away or keep chilled for up to three days in an airtight container.