Heat half of the olive oil in a large frying pan over medium-high heat. Add the onion and cook for 5-7 minutes, until starting to soften. Add the black beans and cook for a further 3 minutes, then add the chilli. Cook for 2 more minutes, then roughly mash with a potato masher or a fork.
Make 4 indents in the bean mash and crack an egg into each one. Season with salt and pepper. Reduce the heat to medium and cook for 5-7 minutes, covering the pan towards the end, if needed, to help the eggs cook.
Meanwhile, make the tomato salsa. Combine the tomatoes, lime juice, garlic and remaining olive oil in a bowl and season to taste.
Heat the corn tortillas according to the pack instructions. Once the eggs are cooked, spoon over most of the tomato salsa, add the avocado slices to the pan, crumble over the feta and sprinkle over the coriander. Enjoy straight away with the corn tortillas.