In a blender, combine the onion, garlic, tomatoes, chilli, lime juice, cumin, chipotle, sugar, salt and pepper. Whiz until almost smooth.
In a large frying pan, heat the blended tomato sauce with the olive oil until some of the liquid bubbles away. Check for seasoning and chilli-heat and adjust to your liking.
Meanwhile, fry the tortillas in a little olive oil until brown and crispy on both sides.
Fry the eggs sunny-side up.
To serve (two tortillas per person), divide the black beans equally among the tortillas, top with the fried eggs, and pour the sauce over. Serve with avocado wedges, chopped green onion, coriander, and a little extra lime juice.