In a pan over medium heat, melt the butter with the olive oil. Add the mushrooms, and season with garlic, oregano, sage, salt, and pepper and cook for three to five minutes — just until they brown and soften. Add in the spinach and cook for one more minute. The spinach should wilt very quickly. Once that's done, you can remove the mixture from the heat and set it aside.
Image Source: POPSUGAR Photography / Hajar Larbah