Deliciously meaty and umami-rich, these portobello "steaks" are simple to throw together for an impressive main dish for any occasion and any season. Don't let the long cooking time intimidate you, there is very little prep and active time required.
Preheat oven to 150°C (300°F). In a large Dutch oven (or oven-safe pot with a lid), add the olive oil, soy sauce, sherry vinegar, tomato paste, coriander seeds and chili flakes along with a generous pinch of salt and a few grinds of black pepper. Whisk to combine.
Add the garlic, shallot and oregano. Arrange the mushrooms, gills facing down, over the aromatics.
Press a piece of parchment paper so that it covers the mushrooms. Place the lid on the pot and move to the oven.
Roast the mushrooms for 1 hour before removing from the oven. Remove the parchment and flip the mushrooms over so that the gills are facing up. Replace the parchment and the lid and cook for a further 15 minutes in the oven.
Transfer the mushrooms to a serving platter, cutting them in half, if desired. Scatter the shallots and the garlic over the mushrooms and drizzle with some of the cooking liquid. Top with chimichurri, if using.