In a mixing bowl, add the drained and rinsed chickpeas. Using a fork or a potato masher, mash the chickpeas until they are mostly broken up but still have some texture.
Add the mayonnaise, celery, red onion, bell pepper, lemon juice, Dijon mustard, garlic powder, salt, and black pepper to the bowl. Mix everything together until well combined.
Taste and adjust seasoning if needed, adding more salt, pepper, or lemon juice based on your preference.
To assemble the sandwiches, place a generous portion of the chickpea salad on a slice of bread or inside a sandwich roll. Top with lettuce and sliced tomatoes if desired.
Close with another slice of bread or the top of the roll. Repeat for the remaining sandwiches.
Serve immediately or refrigerate for later.