Roasted Portobello Steak and Onions

Lighten up this summer and win over the most stubborn of carnivores with Roasted Portobello Steak and Onions. We made ours with farm fresh portobello mushrooms from River Valley Ranch & Kitchens and red onions from Twin Gardens, both at the Schaumburg Farmers Market. Oven roasting these marinated mushroom caps tenderizes while bringing out the meaty umami flavor. Then we pan sear at the end for a bit of char, making this a great addition to our Eat Local Series.

We can sense all the meat-grilling brosefs rolling their eyes and turning their noses up at the thought of a mushroom steak. Embrace your sense of adventure, my dudes, you’ll be glad you did.

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Roasted Portobello Steak and Onions

Roasted Portobello Steak and Onions

  • Author: Fresh. Out.
  • Prep Time: 10
  • Cook Time: 35
  • Total Time: 45 minutes
  • Yield: 4 Servings 1x
  • Category: Entrees, Main Courses
  • Method: Oven Roasting, Pan Searing
  • Cuisine: Vegan


Roasted Portobello Steak and Onions



For the Steaks

  • 4 large portobello mushroom caps, cleaned and stems removed
  • 1 medium red onion, thinly sliced into rings 

For the Marinade

  • 2 tbsp extra-virgin olive oil
  • 2 tbsp coconut aminos*
  • 2 tsp balsamic vinegar
  • 1 tsp red wine vinegar
  • 1/4 tsp garlic powder
  • 1/4 tsp onion powder
  • 1/4 tsp ground cumin
  • 1/4 tsp paprika
  • 1/8 tsp salt (only if using coconut aminos)
  • 1/8 tsp ground coriander
  • 1/8 tsp smoked paprika
  • Generous pinch ground black pepper


  1. In a small measuring cup, combine all marinade ingredients and let sit for 5 minutes.
  2. Break the onion slices into rings and line the bottom of a glass baking dish with half of the rings. Top with the mushroom, cap side up. 
  3. Stir marinade after resting and and gently rub a spoonful of the marinade onto the top of each mushroom cap. Flip the mushrooms gill side up and drizzle the remaining marinade over them. Tilt and swirl each mushroom cap around to distribute the marinade evenly. Lay the remaining onion slices on top of the mushrooms, cover with plastic, and marinate at room temperature for 30 minutes. 
  4. Place oven rack in top position and preheat oven to 400 degrees F. Remove plastic wrap and place baking pan on top rack. Roast 20 minutes, then carefully flip mushrooms to cap side up and roast another 10 minutes. Remove and let rest 5 minutes.
  5. While mushrooms are resting, heat a small saute pan over medium heat and a nonstick or cast iron grill pan over medium-high heat. Brush pans with oil if necessary.
  6. While mushrooms are resting, place the onions in the saute pan to caramelize further, flipping as needed.
  7. Transfer the mushrooms, gill side down to the grill pan to sear, about a minute. Flip to cap side and sear another minute. Transfer mushrooms to a serving platter or individual plates and top with the onions. Serve immediately.


*Do not add salt to marinade if using tamari or soy sauce. Coconut aminos has a sweeter taste with far less salt than soy sauce, so we add a bit of salt to the mix to balance it out. 



Located in Harvard, IL, in Twin Gardens has been family-owned and managed since 1954 and remains focused on delivering the highest quality produce possible. Aside from their roadside stand in Harvard, you can find them at farmers markets spanning from the Chicagoland area to Southern Wisconsin.

Based in Burlington, WI, River Valley Ranch is the oldest mushroom farm in the Midwest, with over 40 years of experience sustainably producing and providing chemical-free foods, including five varieties of mushrooms year-round. River Valley Ranch sells seasonal vegetables and year-round mushrooms at farmers markets in Wisconsin and Illinois, their Farm Store, and the Farmer’s Table, as well as using them in handcrafted food products and farm-to-table cuisine.

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