Preheat the oven to 400°F.

Add the ground beef, egg, cornstarch, Mexican Fiesta seasoning, garlic powder, onion powder, and salt and pepper to a large bowl. Gently mix until just combined, being careful not to overwork the beef.

Form the mixture into medium-to-large meatballs, keeping them relatively uniform in size so they cook evenly.

Heat a drizzle of olive oil in a large oven-safe skillet over medium-high heat. Add the meatballs and sear, turning occasionally, until deeply browned on all sides. They do not need to be completely cooked through at this point. Transfer the meatballs to a plate.

Reduce the heat to medium and add another drizzle of olive oil if needed. Add the chopped bell peppers and onion and sauté for 5–7 minutes, or until tender and beginning to caramelize.

Add the 1½ cans of drained and rinsed black beans, ½ tablespoon Mexican Fiesta seasoning, and 1–2 tablespoons tomato paste. Stir well and cook for another 1–2 minutes.

Nestle the browned meatballs back into the skillet with the vegetables and black beans. Sprinkle 1 cup shredded Mexican-style cheese evenly over the top.

Transfer the skillet to the oven and bake at 400°F for 10–15 minutes, or until the cheese is melted and bubbly and the meatballs have reached an internal temperature of 160°F.

Remove from the oven, top with fresh cilantro, and enjoy!