Place the 114-ounce can chickpeas (drained and rinsed) in a medium bowl.
Add 3 tablespoons hummus to the chickpeas. Using a sturdy fork or potato masher, mash until the mixture reaches your desired consistency.
Taste the mashed chickpeas. Add more hummus as needed (up to a total of 6 tablespoons) for creaminess, and season with sea salt to taste. Stir to combine.
Toast 6 to 8 slices of gluten-free bread.
On half of the toasted slices (3 to 4 slices), evenly spread the mashed chickpea mixture.
Top the mashed chickpeas with the following, dividing evenly among the prepared slices: 1 ripe avocado (peeled and sliced), 1 large vine-ripened tomato (sliced), 2 handfuls mixed greens or spinach, and 1/4 red onion (thinly sliced).
Place the remaining toasted bread slices on top to form sandwiches. Press gently to hold layers together.
Cut each sandwich in half, serve, and enjoy.