In a large mixing bowl, mash 1 can of chickpeas until mostly smooth. Stir in 2 tablespoons of Dijon mustard, 3 tablespoons of mayonnaise, and the juice of half a lemon. Add in 1 finely chopped celery stalk, 0.25 cup diced onions, and a pinch of optional kelp flakes. Mix until well combined and set aside.

Take two slices of hearty bread and spread a generous portion of the chickpea salad mixture on one side of each slice. Optionally, layer on some cheese slices.

Heat a skillet over medium heat and add olive oil or butter. Cook the assembled sandwiches until the bottom is golden brown, about 3-5 minutes. Flip and cook the other side for another 3-5 minutes until crispy and cheese is melted.

Once cooked, remove from the skillet, slice in half, and serve warm with a side salad or chips.