Preheat the oven to 200 degrees. Peel the sweet potato, cut it into equal cubes and spread them over a baking sheet. Drizzle with a small splash of olive oil, season with salt and pepper and toss well. Roast the potato cubes in the oven for about 25 minutes until tender and golden brown.
Meanwhile, prepare the chimichurri. Finely chop the parsley, cilantro, garlic clove and half the red chili pepper. Mix the chopped ingredients in a small bowl with the oregano, red wine vinegar and one tablespoon of olive oil. Season the sauce further with pepper and salt and set aside so the flavors can blend.
Generously season the bavette on both sides with salt and pepper. Heat the remaining olive oil in a frying pan over high heat until the pan is very hot. Cook the meat for about three minutes per side until it has a nice brown crust and is medium-rare inside. Remove the bavette from the pan, place on a cutting board and let the meat rest for a few minutes.
Slice the rested bavette with a sharp knife into thin slices. Make sure to slice against the grain of the meat to keep it tender. Distribute the roasted sweet potato cubes over a plate, place the slices of bavette beside them and spoon the chimichurri over the meat.