Prepare the cucumber, bell pepper, pickled celery, and avocado and combine in a large bowl
In a small bowl, whisk together the oil, vinegar, dijon mustard (if using), garlic powder (if using), and salt and pepper. It should come together to form a dressing
Pour the dressing over the salad and mix to combine until the dressing is evenly coating the vegetables
Serve within 2 hours, or let sit to soak up the flavors
Store in an air-tight container in the fridge for up to 5 days.