Preheat your oven to 400°F and line a baking sheet with parchment paper.
Slice the sweet potato into four 1/2-inch thick rounds, selecting the widest part of the potato for the best bun shape.
Lightly brush both sides of the sweet potato rounds with 0.5 tsp of olive oil and sprinkle with a pinch of sea salt.
Roast the sweet potato rounds for 20-25 minutes, flipping halfway through, until they are tender and the edges are golden brown.
While the potatoes roast, combine the ground beef, garlic powder, remaining sea salt, and black pepper in a bowl, then form into two thick patties.
Heat the remaining 0.5 tsp of olive oil in a cast-iron skillet over medium-high heat and sear the patties for 4-5 minutes per side until cooked through.
Assemble the burgers by placing one sweet potato round down, topping with arugula, a tomato slice, a beef patty, avocado, and the second sweet potato round.