Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Peel and dice the sweet potato into 1/2-inch cubes, then toss them on the baking sheet with 0.5 tbsp of avocado oil, the garlic powder, and a pinch of the sea salt.
Roast the sweet potatoes for 15 minutes, then move them to one side of the pan and add the trimmed asparagus, tossing the spears in the residual oil and heat.
Return the pan to the oven and roast for another 10-12 minutes until the sweet potatoes are golden and the asparagus is tender-crisp.
While the vegetables finish roasting, pat the tuna fillet very dry with a paper towel and season all sides with the remaining sea salt, black pepper, and the sesame seeds.
Heat a cast-iron skillet over medium-high heat with the remaining 0.5 tbsp of avocado oil until it is shimmering but not smoking.
Carefully place the tuna in the skillet and sear for 90 seconds to 2 minutes per side for a perfect medium-rare finish.
Remove the tuna from the pan, let it rest for 2 minutes, then slice and drizzle with coconut aminos before serving with the roasted vegetables.