Grate gruyere cheese and chop sun-dried tomatoes. Add cheese to bread and top with the tomatoes.
Add arugula to a bowl and drizzle with olive oil, a pinch of oregano and a squeeze of lemon. Add on top of the sandwich. Close sandwich.
Heat butter in a skillet. Once melted, add bread to skillet. Cook for about 4-5 min per side on medium to low heat, until cheese is melty and the bread is golden brown. Enjoy!