Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Toss the cubed sweet potatoes and rinsed chickpeas on the baking sheet with 1 tsp of olive oil, smoked paprika, garlic powder, and half of the sea salt.
Spread the mixture in a single layer and roast for 20-25 minutes until the sweet potatoes are tender and the chickpeas are slightly crispy.
Pat the tuna steak dry with a paper towel and season both sides with the remaining sea salt and black pepper.
Heat the remaining 1 tsp of olive oil in a stainless steel or cast iron skillet over medium-high heat until shimmering.
Sear the tuna steak for 1-2 minutes per side for a perfect medium-rare, then remove from the heat to rest for a moment.
In a small bowl, whisk together the tahini and lemon juice with a teaspoon of warm water until smooth and pourable.
Place a handful of fresh arugula on a plate, top with the roasted sweet potato and chickpea mixture, add the sliced tuna, and finish with the zesty tahini drizzle.