Brush both sides of bread slices evenly with 2 tablespoons oil. Cook in a large nonstick skillet over medium heat until golden brown, about 3 minutes per side. Transfer to a plate.
Add mushrooms and the remaining 2 tablespoons oil to the pan; cook over medium-high heat, undisturbed, for 3 minutes. Stir and cook, stirring occasionally, until golden brown and most of the liquid has released, 3 to 4 minutes. Transfer to a bowl.
Meanwhile, stir ricotta, pesto and ⅛ teaspoon pepper together in a small bowl.
Top the toasted bread slices evenly with ricotta mixture, sautéed mushrooms, Parmesan, basil and the remaining ⅛ teaspoon pepper.
