Preheat oven to 400°F.
In a large bowl, toss the tofu and sweet potatoes with the olive oil, cumin, chili powder, smoked paprika, cayenne, salt, and black pepper until evenly coated.
Spread the mixture in a single layer on a baking sheet.
Roast for 25-30 minutes, flipping halfway, until the tofu is crispy and the sweet potatoes are tender.
Remove from oven and stir in the chopped kale and lemon juice.
Serve immediately.