Portobello mushroom burgers are no longer just a sad substitute for beef burgers; they are -legitimately delicious choices on their own.
For charry grilled portobellos that wouldn’t leak moisture and make the buns soggy, we decided to try scoring them, a technique that works well with oven-roasted mushrooms. It worked like a charm on the grill.
We lightly scored the mushrooms on the smooth, non-gill side in a crosshatch pattern. This helped expedite the release of moisture, which dripped out and evaporated on the grill, ensuring intense mushroom flavour and toasty, non-soggy buns. The crosshatching also allowed the mushrooms to absorb more marinade—a flavourful mix of olive oil, red wine vinegar, and garlic.
Once they were cooked, we filled the portobello caps with a savory mixture of feta, sun-dried tomatoes, and roasted red peppers before stacking them on grilled buns with basil mayo, baby arugula, and sweet grilled onions.
If your mushrooms are larger or smaller than 4 to 5 inches, you may need to adjust the cooking time accordingly. If the mushrooms absorb all the marinade, simply brush the onions with olive oil before grilling.
GRILLED PORTOBELLO BURGERS
Start to finish: 50 minutes
4 portobello mushroom caps (4 to 5 inches in diameter), gills removed
1/2 cup extra-virgin olive oil
3 tablespoons red wine vinegar
1 garlic clove, minced
1 teaspoon salt
1/2 teaspoon pepper
4 ounces feta cheese, crumbled (1 cup)
1/2 cup jarred roasted red peppers, patted dry and chopped
1/2 cup oil-packed sun-dried tomatoes, patted dry and chopped
1/2 cup mayonnaise
1/2 cup chopped fresh basil
4 (1/2 inch-thick) slices red onion
4 kaiser rolls, split and toasted
1 ounce (1 cup) baby arugula
Cut 1/16 inch-deep slits on top of mushroom caps, spaced 1/2 inch apart, in crosshatch pattern. Combine mushrooms, oil, vinegar, garlic, salt, and pepper in 1 gallon zipper-lock bag, seal bag, and turn to coat. Let sit for at least 30 minutes or up to 1 hour.
Combine feta, red peppers, and sun-dried tomatoes in bowl. Whisk mayonnaise and basil together in separate bowl. Push 1 toothpick horizontally through each onion slice to keep rings intact while grilling.
‚Äî For a charcoal grill: Open bottom vent completely. Light large chimney starter filled with charcoal briquettes (6 quarts). When top coals are partially covered with ash, pour evenly over grill. Set cooking grate in place, cover, and open lid vent completely. Heat grill until hot, about 5 minutes.
‚Äî For a gas grill: Turn all burners to high, cover, and heat grill until hot, about 15 minutes. Turn all burners to medium-high.
Clean and oil cooking grate. Remove mushrooms from marinade, and brush onions all over with remaining mushroom marinade. Place onions and mushrooms, gill side up, on grill. Cook (covered if using gas) until mushrooms have released their liquid and are charred on first side, 4 to 6 minutes. Flip mushrooms and onions and continue to cook (covered if using gas) until mushrooms are charred on second side, 3 to 5 minutes.
Transfer onions to platter and discard toothpicks. Transfer mushrooms to platter, gill side up, and divide feta mixture evenly among caps, packing down mixture. Return mushrooms to grill, feta side up, and cook, covered, until heated through, about 3 minutes.
Return mushrooms to platter and tent with aluminum foil. Spread basil mayonnaise evenly over roll bottoms and top each with 1 mushroom and 1 onion slice. Divide arugula evenly among burgers, then cap with roll tops. Serve.