If using a Traeger, preheat your grill to 500F. If using a charcoal or gas grill, set up a direct, high heat.
Place the sweet potatoes on the hottest part of the grill and cook, turning regularly, until completely charred and fork-tender, around 45 minutes depending on their size. Transfer to a bowl and cover with foil to keep warm.
Drizzle the zucchini with olive oil and lightly season both sides with salt and pepper to taste. Transfer the zucchini to the grill and cook until grill marks form, around 4 minutes. Flip and cook the other side until grill marks form and the centre is tender, around 4 more minutes. Transfer to a platter and cover with foil to keep warm.
Place the red peppers on the grill, skin-side down, and cook until completely charred, around 6 minutes. Transfer to a bowl and cover to steam for 5 minutes to make peeling the skin easier. Using the back of a knife or your hands, peel away the charred skin from the peppers. Alternatively, you can grill the peppers whole and deseed after cooking. Transfer the peppers to the platter with the zucchini and cover with foil to keep warm.
Slice the picanha into 1.5” steaks, with the grain. Generously season both sides with salt and grill over direct heat until grill marks form, around 4 minutes. Flip and cook the other side until grill marks form and the thickest part of the steaks registers 135F for a medium centre. Transfer the steaks to a board and let them rest 8 minutes before slicing against the grain. Serve the picanha with the chimichurri and grilled vegetables.