Heat a small drizzle of olive oil or use cooking spray in a medium skillet over medium-high heat. Add the crushed garlic and cook until fragrant, about 30–60 seconds; remove from heat and transfer garlic to a small bowl.
Add the ricotta, thawed and drained spinach, grated Parmesan, sea salt, cracked pepper, and dried Italian herbs to the bowl with the garlic and stir until well combined.
Spread butter on one side of each bread slice. On the un-buttered side of two slices, divide the ricotta mixture evenly, then top each with half the mozzarella. Close sandwiches with the remaining bread, buttered side out.
Return the skillet to medium heat. Place the sandwiches in the skillet and cook until golden brown and the cheese melts, about 3–4 minutes per side, flipping once.
Slice and serve hot, sprinkled with extra Italian herbs if desired, with pasta sauce on the side for dipping.