Clean mushrooms by rinsing gently in water and patting dry. Place mushroom caps on a baking sheet, gill-side up. Drizzle with 2 tbsp olive oil, turn mushrooms, and drizzle with remaining 2 tbsp olive oil. Season with sea salt and black pepper and toss to coat.
Roast mushrooms for 25 minutes. Turn mushrooms and continue to roast until larger mushrooms are crisp on edges and smaller ones are crisp throughout, 10-15 minutes more. Season with more salt and pepper to taste. Serve warm or at room temperature.