1In a medium bowl, mash the chickpeas with a fork or potato masher until they are mostly broken down but still have some texture.
Add the diced celery and red onion to the mashed chickpeas and mix well.
Stir in the vegan mayonnaise, Dijon mustard, lemon juice, garlic powder, and onion powder until everything is well combined.
Season with salt and pepper to taste.
Toast the whole grain bread slices if desired.
Spread the chickpea salad mixture evenly onto two slices of bread.
Top with the remaining slices of bread to form sandwiches.
Serve immediately or refrigerate for later use.