Preheat the oven to 200°c /gas mark 6/ 390°F. Peel and grate the sweet potato. Whisk the egg in a bowl. Add the grated sweet potato, garlic, parsley, salt and pepper. Mix until combined.
Line a baking tray with greaseproof paper. Divide the potato mixture into two equal parts and place on the oven tray. Form the rösti around 10 cm in diameter and 2,5 cm high. Bake in the oven for 25-30 minutes, until golden.
Combine all salsa ingredients in a bowl except honey. Taste and add honey if needed depending on how sweet the tomatoes are. Add salt and pepper to taste. Set aside
Bring a small pan filled with 2/3 full of water to the boil.
Once boiling, bring down to a simmer. Add the vinegar and create a whirlpool in the water by whisking with a whisk. Crack the eggs in a small cup, one at the time. Gently add the egg to the simmering whirlpool and poach for 3-4 minutes, depending on how large the egg is. Lift up the egg with a slotted spoon after 3 minutes. Prod the egg, the egg white should be firm but were the egg yolk is it should be soft. Once done, remove from the water and place on kitchen roll.
Remove the rostis from the oven and gently remove them from the greaseproof paper.
Assemble the rostis by adding sliced avocado, black bean salsa and top with the poached egg. Finish with chilli flakes, fresh parsley or coriander/cilantro