Preheat the oven to 450°F and line a baking sheet with parchment paper. Slice the peppers in half lengthwise, remove the seeds and membranes, and place on the baking sheet, cut side up. Drizzle with olive oil, salt, and pepper and bake 10 minutes. Tip out and discard any liquid that pools inside the peppers. Set the peppers aside.
Make the filling. In a large bowl, mix together the olive oil, garlic, jalapeños, scallions, lime zest, lime juice, cumin, coriander, cayenne, salt, and cilantro. Fold in the rice, black beans, and corn.
Scoop the filling into the pepper halves and top them with the cheese. Broil for 2 to 5 minutes or until the cheese is bubbling and browned. Alternatively, continue baking at 450°F for 10 to 15 minutes until the cheese is melted. Serve with the avocado slices, lime wedges, and extra jalapenos, if desired.