Portobello Sandwich Recipe

Preheat the oven broiler to high or set oven to 450°F (230°C). Line a baking sheet with foil.

Place whole red bell peppers on the baking sheet, brush lightly with 1 tbsp olive oil and sprinkle 1/4 tsp salt.

Broil or roast until skins are charred and blistered on all sides, turning peppers every 5–7 minutes, about 15–20 minutes total.

Transfer hot peppers to a bowl and cover tightly with plastic wrap or place in a sealed zip-top bag to steam for 10–15 minutes (this loosens skins).

Peel off skins, remove stems and seeds, then slice peppers into 1/2-inch strips. Set aside.

While peppers roast, heat 1 tbsp butter and 1 tbsp olive oil in a large skillet over medium-low heat.

Add the thinly sliced onions, 1/2 tsp salt and 1/4 tsp pepper. Stir to coat and spread them evenly in the pan.

Cook slowly, stirring every 4–5 minutes, adjusting heat as needed to prevent burning. After about 15 minutes add 1/2 tsp brown sugar to encourage caramelization.

Continue to cook until onions are deep golden brown and soft, about 25–30 minutes total. Remove from heat and keep warm.

Clean portobello caps by wiping with a damp cloth and remove stems. If desired, scrape out gills with a spoon for a milder flavor.

Mince 2 cloves garlic and combine with 3 tbsp olive oil, 1 tbsp balsamic vinegar, 1 tsp fresh thyme, 1 tsp salt and 1/2 tsp black pepper in a shallow dish or bowl to make the marinade.

Place mushroom caps gill-side down in the marinade and brush tops and undersides. Let marinate 10–15 minutes, turning once to coat evenly.

Heat a grill pan or outdoor grill to medium-high (about 400°F / 200°C). Oil the grates lightly.

Grill mushrooms 4–6 minutes per side, brushing with remaining marinade, until tender and slightly charred. Alternatively, roast on a baking sheet at 425°F (220°C) for 15–20 minutes, flipping once.

Remove mushrooms and let rest 3 minutes, then slice each cap into 1/4–1/2-inch thick pieces or leave whole for a heftier sandwich.

Split ciabatta rolls and lightly brush cut sides with 1 tsp olive oil. Toast on the grill or in a skillet until golden, 1–2 minutes.

If using the optional mayo spread, mix 2 tbsp mayonnaise with 1 tbsp of softened goat cheese to create a creamy spread; otherwise, simply spread goat cheese directly on both cut sides (about 1.5 oz per roll).

On the bottom half of each roll, layer baby arugula (about 1/2 cup), then place grilled portobello slices (or a whole cap), followed by 2–3 strips of roasted red pepper and a generous portion of caramelized onions (about 2–3 tbsp).

Crumble or slice remaining goat cheese over the top (about 1.5 oz per sandwich). Add fresh basil leaves (2 per sandwich). Drizzle 1/4 tbsp balsamic glaze over filling if desired.

Top with the other half of the roll, press gently, slice in half, and serve immediately.