Butter one side of a piece of bread with the softened butter and place butter-side down in a medium non-stick skillet over medium heat.

Add a slice of cheese to the bread and spoon ¼ of the beef, ¼ of the diced tomatoes, and ¼ of the diced peppers on the cheese.

Lay ¼ of the avocado slices over the top and top them with another slice of cheese.

Butter one side of another slice of bread and place it butter-side up on top of the cheese, cook until cheese begins to melt and bread turns a golden brown, flip and cook the other side until cheese is melted through.

Repeat for other sandwiches.