Smoky Flank Steak Tacos

Name: Smoky Flank Steak Tacos
Ingredients: 1 ½ teaspoons smoked paprika; ¾ teaspoon ground cumin; ½ teaspoon ground cinnamon; ¼ teaspoon cayenne; 3 ½ teaspoons kosher salt, divided; 1 pound flank steak; 1 tablespoon olive oil, plus more for grill grates; 1 medium red onion, sliced, root ends left intact; ¼ teaspoon freshly ground black pepper; 2 cups cherry tomatoes, quartered; ½ cup fresh cilantro leaves and tender stems, plus more for serving; 3 tablespoons fresh lime juice (from 2 limes), plus wedges for serving; 1 serrano chile, seeded and finely chopped; 8 6-in. corn tortillas