Vegetarian Bean and Cheese Enchiladas

olive oil

medium yellow onions, finely chopped

red bell pepper or poblano chile, stemmed, seeded and cut into 1/4-inch pieces

garlic cloves, peeled and thinly sliced

Kosher salt and black pepper

ground cumin

fire-roasted tomatoes, preferably crushed (see Tip)

chili powder

hot sauce or 1 chipotle chile in adobo, chopped (optional)

sour cream, plus more for serving, optional

black beans, rinsed

mild Cheddar or Monterey Jack cheese, grated (about 1 1/4 cups)

to 12 (6-inch) soft corn or flour tortillas

Fresh cilantro leaves and stems, for serving