In a small bowl, combine the ricotta cheese, chopped sun-dried tomatoes, dried oregano, garlic powder, and black pepper. Mix gently until just combined. Set aside.

Lightly wilt the fresh spinach. You can do this by tossing it in a dry, hot pan for 30 seconds, or microwaving it briefly until just softened. Squeeze out any excess moisture and roughly chop.

Spread the ricotta mixture evenly over two slices of sourdough bread. Top the ricotta mixture with the wilted spinach, distributing it evenly.

Place two slices of provolone cheese on top of the spinach layer on each sandwich half. Close the sandwiches with the remaining two slices of bread.

Generously spread the softened butter on the exterior sides of all four slices of bread.

Heat a large non-stick skillet or griddle over medium-low heat. Place the sandwiches on the hot skillet. Cook for 5-6 minutes per side, pressing down gently with a spatula occasionally, until the bread is deeply golden brown and the cheese is fully melted.

Remove from the heat, slice diagonally, and serve immediately.