Vegan Barbacoa Fajitas

For pickled onions, place onion slivers in a bowl. Add lime juice and salt; toss to combine. Press down on onion with the back of a fork. Cover; chill at least 2 hours or up to 3 days. Drain before serving. 2. For sauce, in a blender combine broth, 2 tablespoons of the vinegar, and the next six ingredients (through oregano). Cover and blend until smooth. Transfer to a medium saucepan. 3. Combine the remaining 1 tablespoon vinegar and 2 tablespoons water. Brush over mushrooms and bell peppers. Grill vegetables, uncovered, over medium-high 8 to 10 minutes or until tender and slightly charred, turning as needed and brushing with additional vinegar mixture to prevent drying. 4. Transfer mushrooms and peppers to a cutting board. Cut into strips. Transfer mushroom strips to pan with sauce; stir to coat. Simmer mushrooms and sauce over medium 3 to 5 minutes or until sauce is slightly thickened. 5. Serve mushrooms, peppers, and pickled onions with tortillas and desired toppings.