Balsamic Portobello Burgers with Caramelized Onions & Roasted Sweet Potatoes

  • Author: Emily Weeks, RDN, LD
  • Prep Time: 15 minutes
  • Cook Time: 30 minutes
  • Total Time: 45 minutes
  • Yield: Makes 2 burgers 1x


A burger so good, you wouldn’t even know it’s vegan! Portobello mushrooms are marinated in a savory sauce, then sauteed until soft. Balsamic portobello burgers are topped with caramelized onions, fresh tomato, and slathered in vegan aioli.



  • 1 lb sweet potato
  • 1 tsp extra virgin olive oil
  • ½ tsp paprika
  • ½ tsp salt
  • ¼ tsp black pepper
  • 2 caps portobello mushrooms
  • 2 cloves garlic
  • 2 tbsp extra virgin olive oil
  • 2 tbsp balsamic vinegar
  • 1 tsp Italian seasoning
  • 1 medium yellow onion
  • 1 tbsp extra virgin olive oil
  • ¼ tsp salt
  • 2 tbsp vegan mayonnaise
  • 1 tsp extra virgin olive oil
  • ½ tsp Dijon mustard
  • ¼ tsp garlic powder
  • ¼ tsp salt
  • ½ head butter (Boston) lettuce
  • 1 tomato
  • 2 whole grain buns or rolls


  1. Preheat oven to 400°F.
  2. Peel the sweet potatoes and cut into 1-inch pieces. Transfer to a large bowl; add 1 tsp oil, paprika, salt, and pepper, toss to coat. Add potatoes to a baking sheet and bake, until softened, about 20-25 minutes. Reserve bowl for later use.
  3. Dry the mushrooms; remove the stems and carefully scrape out the gills. Peel and mince the garlic.
  4. In the large bowl, whisk together the 2 Tbsp oil, vinegar, Italian seasoning, and garlic. Add the mushrooms and toss to coat; set aside.
  5. Peel and slice the onion into half rings.
  6. Heat a medium saucepan over medium heat. Once the saucepan is hot, add 1 Tbsp oil and swirl to coat the bottom. Add the onion and salt to the saucepan; cook, stirring occasionally, until browned and softened, 15-20 minutes.
  7. In a medium bowl, whisk together the mayonnaise, olive oil, Dijon, garlic powder, and salt. Set aside.
  8. Preheat a skillet over medium-high heat. Once the skillet is hot, add the mushrooms. Cook, stirring occasionally, until softened, 3-5 minutes per side. Discard leftover marinade.
  9. Separate the lettuce head into leaves. Slice the tomato.
  10. To serve, spread the mayonnaise mixture on buns. Top with tomato slices, lettuce, mushrooms and caramelized onions. Serve the roasted sweet potatoes on the side. Enjoy!