In a large bowl, toss kale (stems and thick ribs removed) with oil, lemon juice and salt.
Arrange in a single layer on 2 large, rimmed, parchment-paper-lined baking sheets.
Bake in a preheated 350°F (180°C) oven, tossing kale and rotating baking sheets halfway through, until kale is dark green and almost crisp, 15 to 20 minutes.
Sprinkle with lemon zest and hot pepper flakes; toss gently and let cool on baking sheets.
Baking tip: Watch closely toward end of bake time and remove from oven when almost crisp – “chips” will crisp even more as they cool. But if any are still a bit soft after being out of the oven for more than 10 minutes, return them to the oven and continue baking for a few minutes longer.
Nutrition information (per serving): 93 calories, 4 g protein, 4 g fat (1 g saturated fat), 14 g carbohydrates, 3 g fibre, 0 mg cholesterol, 155 mg sodium