For the dry rub: In a mixing bowl, combine the chili powder, Spanish paprika, brown sugar, cumin, kosher salt, black pepper and cayenne.
For the BBQ sauce: Saute the onions in the butter and, when opaque, add the beef stock, ketchup, chipotle, apple cider vinegar and 3 tablespoons of the dry rub. Bring to a boil, lower the heat and simmer for 15 to 20 minutes. Blend until smooth.
For the sorrel compound butter: Combine the butter, sorrel and salt until well incorporated.
For the veggie sandwich: Preheat an outdoor grill or indoor grill pan.
In a large mixing bowl, toss the mushroom caps and zucchini slices with olive oil and some dry rub. Place on the grill and cook on all sides, turning occasionally, until great grill marks are made.
In a mixing bowl, toss the baby green onions with olive oil. Add them to the grill and cook until charred on all sides.
To assemble the sandwiches, slather the bread with sorrel compound butter. Then add the mushroom caps and zucchini slices. Top with the green onions and drizzle with Texas BBQ sauce.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.