Preheat the air fryer: Set it to 390°F (200°C) for 3–5 minutes. A hot basket helps the veggies crisp.
Prep the sweet potatoes: Toss cubes with 1 tablespoon oil, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/2 teaspoon garlic powder, and the smoked paprika.
Coat evenly.
Start the sweet potatoes: Add to the air fryer in a single layer. Cook for 8 minutes, shaking halfway. They should be starting to brown but not fully tender yet.
Prep the broccoli: While the sweet potatoes cook, toss broccoli florets with remaining 1 tablespoon oil, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/2 teaspoon garlic powder, and onion powder if using.
Add the broccoli: After the first 8 minutes, shake the basket, then add the seasoned broccoli on top.
Keep it as even as you can. If your basket is small, cook in two batches instead of overcrowding.
Finish cooking: Air fry for 7–9 more minutes at 390°F, shaking once. The sweet potatoes should be tender and caramelized; the broccoli should have crisp tips and bright green stems.
Finish with brightness: Transfer to a bowl.
Toss with lemon juice (and zest, if using). Add red pepper flakes and Parmesan or nutritional yeast to taste.
Taste and adjust: Add a pinch more salt or pepper if needed. Serve hot.