01 - Set the oven temperature to 400°F and place a large ovenproof skillet or cast-iron pan inside to warm.
02 - Heat olive oil in a large sauté pan over medium heat; cook the sliced onion for 3 to 4 minutes until softened.
03 - Incorporate minced garlic and continue cooking for an additional minute, stirring frequently to prevent burning.
04 - Add chopped kale, sea salt, black pepper, and crushed red pepper flakes if desired. Sauté while tossing regularly until the kale wilts and turns bright green, about 4 to 5 minutes.
05 - Carefully remove the hot skillet from the oven and evenly spread the sautéed kale mixture inside. Return the skillet to the oven and bake for 10 to 12 minutes until the edges develop slight crispness.
06 - Remove from oven, drizzle with lemon juice, and garnish with toasted pine nuts if using. Serve immediately.