Preheat oven to 450°F. Combine sweet potatoes, poblanos and onion wedges in a large bowl. Add 2 tablespoons oil, ¾ teaspoon smoked paprika and ½ teaspoon each salt and cumin; toss to coat. Spread in an even layer on a large rimmed baking sheet. (Reserve the bowl; do not wipe clean.)
Roast, tossing once, until the vegetables are starting to brown and the sweet potatoes are tender, 25 to 30 minutes. (If desired, increase oven temperature to broil during the final 3 minutes of cooking to char the mixture.) Let cool slightly on the baking sheet, about 10 minutes.
Meanwhile, scoop avocado flesh into a medium bowl; add 2 tablespoons lime juice, 1 tablespoon cilantro, the grated garlic and the remaining ½ teaspoon salt. Mash and stir to reach desired consistency.
In the reserved large bowl, combine the remaining 1 tablespoon oil, 1 tablespoon lime juice and ¼ teaspoon each smoked paprika and cumin. Add rinsed black beans; toss to coat.
Divide the avocado mixture among 4 shallow bowls (about ⅓ cup each); spread to cover the bottoms of the bowls. Top each bowl with about 1¼ cups vegetable mixture, about ⅓ cup beans, 2 teaspoons cotija and 1 teaspoon pickled onion. Garnish with cilantro leaves and serve with lime wedges, if desired.
