Sauté onion in hot oil until translucent, add garlic and cook until lightly browned. Incorporate black beans and mash, season with salt to taste, refry beans until slightly dry and spreadable, remove from heat and reserve.
Mix red onion, cherry tomatoes, cilantro, serrano chili, lime juice, season with salt and pepper to taste and reserve.
Fry the chorizo in hot oil until golden brown, remove from heat and reserve.
Spread bread slices with refried beans, sprinkle with cheese and top with chorizo, broil until cheese is bubbly and golden brown, remove from broiler. Serve with pico de gallo