4 large Portobello mushrooms, gills and stems separated
1 (200g) jar oil-packed sun-dried tomatoes
¼ cup grated cheese
1 medium shallot
3 tbsp olive oil, divided
½ tsp kosher salt
¼ tsp freshly ground black pepper
140g baby spinach (5 packed cups)
Method
Hollow out the mushrooms and chop the gills and stems very finely.
Arrange a rack in the top third of the oven and heat the oven to 205°C.
Drain one jar of oil-packed sun-dried tomatoes well, pat dry with towels, and thinly slice if needed.
Finely chop one medium shallot and add to cart the chopped stems.
Brush the mushrooms on both sides with 2 tablespoons of the olive oil and season with salt and black pepper. Place the mushrooms on a rimmed baking sheet stem-side down and roast until just beginning to soften, about 10 minutes. Meanwhile, make the filling.
Heat the remaining 1 tablespoon olive oil in a large skillet over medium heat until shimmering. Add the shallot and sauté until softened and translucent, 1 to 2 minutes. Add the baby spinach and toss until just wilted, about 1 minute. Remove the pan from the heat. Stir in the sun-dried tomatoes.
Remove the baking sheet from the oven and flip the mushrooms over with a flat spatula. Divide the spinach mixture evenly among the mushroom caps, then sprinkle with the grated cheese.
Roast until the mushrooms are tender and the cheese just starts to melts, about 10 minutes. Switch the broiler on and grill until the cheese browns, 2 to 3 minutes more.