Mix the patty ingredients and then gently form four patties of equal size, each about 2 centimetres thick. With your thumb or the back of a spoon, make a shallow indentation about 2.5 centimetres wide in the centre of the patties to prevent them from forming a dome as they cook. Refrigerate the patties until ready to grill.
Related Grill Skills
Prepare the grill for direct cooking over medium–high heat (200ºC to 260ºC).
In a large skillet over medium heat on the stove, warm the vegetable oil, sesame oil and 1 teaspoon of the chili–garlic sauce. Gradually add the spinach by the handful and stir just until it begins to wilt, 2 to 3 minutes. Remove from the heat and add the sesame seeds.
Combine the ketchup with the remaining 2 tablespoons chili–garlic sauce.
Grill the patties over direct medium–high heat, with the lid closed, until cooked to medium doneness (70ºC), 8 to 10 minutes, turning once. During the last 30 seconds to 1 minute of grilling time, toast the buns, cut-side down, over direct heat.
Build each burger on a bun with chili–garlic ketchup, a patty and sesame spinach. Serve warm.