Combine the soy sauce, water, sugar, mirin, ginger, garlic, cornstarch, and chili-garlic sauce in a small saucepan over medium-high heat. Simmer until the mixture thickens and reduces to about 3/4 cup, 5 to 7 minutes, then transfer to a bowl.

Spread the tofu planks across a paper towel–lined baking sheet and let them drain for 20 minutes. Gently press the tops dry with additional paper towels to remove surface moisture, which helps the tofu sear correctly.

Brush both sides of the tofu with oil and season with salt and pepper.

Prepare the grill. For charcoal, build a two-level fire by concentrating the coals on one side; for gas, heat all burners to high for 15 minutes.

Clean and oil the cooking grate. Place the tofu on the grill perpendicular to the grate bars and cook until lightly browned on both sides, 6 to 10 minutes total, using two spatulas to flip the pieces gently halfway through.

Move the tofu to the cooler part of the charcoal grill or reduce gas burners to medium. Brush the top of each piece with glaze and cook for 1 to 2 minutes, then flip, brush the other side, and cook until the glaze is well-browned and bubbling.

Transfer the tofu to a platter, brush with the remaining glaze, and sprinkle with cilantro. Serve hot with rice or greens.