Preheat the oven. Set to 500°F.
Wipe mushrooms clean and remove stems. Lightly spray with olive oil. Season with salt + black pepper.
3 large portobello mushrooms, olive oil spray, 1 teaspoon salt, ¼ teaspoon black pepper
Place on a baking sheet and roast for 4 minutes per side.
Heat olive oil in a skillet over medium. Add garlic and red onion; cook until softened. Add spinach and cook until just wilted. Season with salt and pepper.
1 teaspoon salt, 3-4 cups fresh spinach, 2 tablespoons olive oil, 3-4 teaspoons minced garlic, ½ cup red onion or shallot, ¼ teaspoon black pepper
Spoon spinach mixture into mushroom caps.
Broil for 2–3 minutes (optional).
Garnish with pine nuts, nutritional yeast flakes and red pepper flakes if you like. Serve warm
¼ cup nutritional yeast flakes, toasted pine nuts