Grilled Beef Barbacoa Tacos

Name: Grilled Beef Barbacoa Tacos
Ingredients: 2 small red onions; 1 plum tomato, halved lengthwise; 1/4 cup vegetable oil, plus more for drizzling; Kosher salt and freshly ground black pepper; 1/3 cup fresh cilantro leaves and stems, roughly chopped; 2 teaspoons smoked paprika; 2 teaspoons light brown sugar; 3/4 teaspoon ground cumin; 1/2 teaspoon dried oregano; 2 cloves garlic, chopped; 2 medium chipotle peppers in adobo; 3/4 cup plus 1 tablespoon cider vinegar; 3 pounds beef chuck roast, cut into 2-inch chunks; Grilled corn tortillas, for serving; Suggested garnishes: sliced avocado, cilantro leaves, sour cream