Stuffed Portobello Burgers With Caramelized Onions

By Matthew Kadey, MS, RD
May 17, 2018

Fungi. Ewww. That’s true if it’s fuzz on your loaf of bread or mold in the corners of the gym shower. But mushrooms, redolent of the earth and presenting in a dizzying array of shapes, are fruiting bodies worth cozying up to.

In terms of nutrition, mushrooms are a stand-out source of certain potent antioxidants—including ergothioneine and glutathione—that may exert disease-fighting prowess via their power to fend off cell-damaging free radicals. Now, food scientists have uncovered the best way to cook mushrooms to preserve their nutritional might.

In a study published in the International Journal of Food Sciences and Nutrition, white button, shiitake, oyster and king oyster mushrooms that were grilled or (surprise!) microwaved maintained significantly higher antioxidant activity than those that were boiled or fried. That’s probably because antioxidants leach into water or oil, whereas dry cooking does a good job of keeping them where they belong.

So, get outside and fire up the grill to cook meaty portobello mushrooms. Packed with umami flavor, these meatless burgers won’t leave you asking, “Where’s the beef?” Serves 4.

1 T unsalted butter

1 large yellow onion, sliced into thin rounds

1 T sugar

1 t balsamic vinegar

1 C sliced roasted red peppers

8 large portobello mushrooms, stems removed and gills scraped out

4 slices manchego, provolone or mozzarella cheese

2 C baby spinach

4 whole-grain buns

Melt butter in large skillet over medium heat. Add onions and cook until translucent, about 5 minutes. Stir in sugar and balsamic vinegar. Reduce heat to medium-low, cover pan and cook for 30 minutes, stirring occasionally or until onions are very soft and a dark golden color.

Preheat grill to medium. Brush mushrooms with oil, and season with salt and pepper to taste. Add mushrooms to grill, stem sides down, and cook for 5 minutes. Flip mushrooms and cook for another 4 minutes. Top four mushrooms with equal amounts of red peppers, cheese and spinach. Cover with remaining mushrooms, stem sides down. Cook for 1 minute or until cheese has melted. Heat buns on grill for 1 minute or until toasted.

Top bun bottoms with stuffed mushrooms, caramelized onions and bun tops.

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Matthew Kadey, MS, RD

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