Preheat the oven to 390°F.
Toast the bread: Spread 2 tbsp unsalted butter evenly on 12 slices of sprouted wheat bread.
Bake the bread: Put them on a baking rack and bake on the bottom shelf of the preheated oven for 3 minutes. Remove from the oven and set aside.
Cook the chicken: In a cast iron skillet on medium heat, add 17 oz skinless, boneless chicken breast, 2 tbsp olive oil, 1/4 tsp salt, 1/2 tsp black pepper, 1 tsp paprika, and 1/2 tsp oregano. Cook for 3 minutes, stirring occasionally.
Assemble the sandwiches: Build each sandwich in this order: A slice of bread, Greek yogurt, romaine lettuce, sliced tomato, ham, cheddar cheese, cooked chicken, another bread slice, yogurt, romaine lettuce, red onion, chicken, coriander, and top it off with a final bread slice. Repeat with the remaining ingredients and you will have 4 sandwiches in total.
Garnish and serve: Press down firmly to pack all the ingredients together. Garnish by piercing cocktail toothpicks into the sandwiches and cutting them in half diagonally. If you’re packing these sandwiches to go, cut them in half and wrap each portion in parchment paper.