In a skillet, heat olive oil over medium heat and sauté garlic for 30 seconds. Add spinach and a pinch of salt. Cook until wilted (about 2 minutes). Set aside.
Spread ricotta cheese evenly over two slices of bread. Top with sautéed spinach, chopped sun-dried tomatoes, and mozzarella. Season with a bit of pepper.
Top each with the remaining slices of bread. Butter the outsides of the sandwiches.
Heat a nonstick skillet or griddle over medium heat. Place the sandwiches in the skillet, pressing slightly with a spatula. Grill 3–4 minutes on each side, until golden brown and cheese is melted.
Slice and serve immediately while hot and gooey.