Preheat the oven to 375ºF (191ºC).

Cut the tops off of each bell pepper, leaving about 3 inches of the bottom for stuffing. Remove the membrane and seeds. Chop the top pieces into ¼" dice, about 1 cup. Set aside.

Grease the sides and bottom of a cast-iron skillet or casserole baking dish with olive oil. Arrange the peppers inside and lightly season the insides with salt and pepper.

Chop the onion into ¼" dice. Mince the garlic and serrano pepper.

Heat a large skillet over medium-high heat. Add 1 tablespoon of olive oil. Once hot, add diced onion, minced garlic, and minced serrano pepper. Saute until tender, about 3 minutes.

Add in the ground beef, breaking it into smaller pieces. Cook until no longer pink, about 4 minutes. Season with cumin, salt, black pepper, smoked paprika, and chili powder, and stir to combine.

Add in 1 cup of diced bell peppers, and saute for 1 minute. Add in black beans, corn, tomatoes, and green onion, stir, and cook for 1 minute.

Turn off the heat and add in ¾ cup cheese, stir to combine. Taste the beef filling and add more salt and pepper as needed.

Add about ¾ cup of filling to each bell pepper.

Bake until the peppers are tender when pierced with a fork, about 30 minutes. Remove from the oven and sprinkle about 1 teaspoon of cheese on top of each pepper. Bake until the cheese is melted, about 2 minutes.

Serve garnished with green onions and thinly sliced serrano peppers.