Place 2 tablespoons olive oil, 3/4 teaspoon kosher salt, 1/2 teaspoon dried thyme, 1/4 teaspoon garlic powder, and 1/4 teaspoon black pepper in a large bowl and whisk to combine.
Cut 1 head cauliflower in half and cut out the tough core. Cut the florets into 1- to 1 1/2-inch pieces (6 to 7 cups). Transfer to the bowl and toss until evenly coated.
Heat an air fryer to 390°F to 400°F. Arrange the cauliflower florets in an even layer in the basket or tray of a 5 1/2-quart or larger air fryer. Air fry, tossing every 5 minutes, until the cauliflower is tender with browned and crispy edges, about 15 minutes total.