In a small pan over medium high heat, heat olive oil. Add in red onions and soften for 1-2 minutes, add in cilantro and cook for 30 seconds. Remove from heat.

Assemble sandwiches by laying two slices of bread side by side, add in half of the ingredients to one slice of bread and cover with the other slice. Repeat for the other two slices.

Melt butter over medium heat in a pan, add in one sandwich and allow to cook 2-3 minutes or until a golden color and flip and repeat. Do the same for the other sandwich, adding more butter if needed.